Electricity

TEACHER’S GUIDE

SUBJECT : PHYSICS

TOPIC : ELECTRICITY

SUBTOPIC : DOMESTIC ELECTRICITY ENERGY CONSUMPTION

CLASS : SENIOR FOUR

TIME REQUIRED : MINIMUM 240 MINUTES, MAXIMUM 360 MINUTES

Brief description

This unit deals with safe and economical ways of using electricity in our homes. It explores both domestic and energy consumption and how through understanding how electric energy is generated during domestic use money can be saved.

Electrical energy is the most environmentally friendly form of energy, as no green house gases or pollutants are emitted during its use. Increased use of electricity would save/reduce the destruction of forests and its negative impact on the environment. However, the electrical energy produced is limited hence leading to high-energy bills, which in many cases are difficult to understand by many customers.

As such, there is need to sensitise the electricity energy users on how to save on the energy used by the household. At the same time those who are not currently using electricity should be enabled to use it. It is hoped that the learners should be able to interpret energy bills and advocate prudent energy usage in their homes and channel savings to other development needs.

Objectives

By the end of these activities the learners should be able to:

1. Read an electricity bill and establish its authenticity, owner, and time frame.
2. Interpret correctly the terms used in the bill
3. Calculate correctly the payment arrived at in the bill.
4. Read and interpret correctly the rating written on an electrical appliance.
5. Estimate energy consumed by an electrical appliance in a period of time.
6. Suggest ways of economical energy consumption in the home with the aim of reducing energy bills.

Teaching / learning aids

• Energy savers
• Filament bulbs
• Power source
• Electricity bills

Methodology

Group work

Demonstration

Discussion

Job- related life skills

In forming the groups ensure that the following skills are deliberately achieved.

Personal attributes - interpersonal, relationship, persuasion, leadership and creativity.

Communication – communication.

Team working - team work.

Problem solving – analysis.

Application of Number – numeracy.

Information skills – observation

CONTENT

Electricity and Energy Usage in the home

Activity One

Procedure

1. Give the learners a 100W filament bulb.
2. Ask them to describe markings on the bulb.
3. Ask them to calculate the energy used by the bulb when it works for 10hours in joules and then in kWh.
4. Ask one of the learners to demonstrate on the chalkboard how s/he has calculated kWh.

Activity Two

1. Divide the learners in into groups of 4-8 and ask them to discuss the definition of the kilowatt-hour.
2. Encourage participation of all learners.
3. Monitor / supervise the discussions and make the clarification as needed /appropriate.
4. Recap the key ideas with the whole class.

Activity Three

In their groups ask the learners to study the energy bill provided and describe the following;

1. Features that show that the bill is genuine.
2. Features that identify the owner.
3. Features that give the time frame of the bill.
4. The meter readings taken.
5. How the bill is calculated.

Ask the group to make a record of their findings.

Activity Four

Ask the learners to study the marking on the energy saver and filament bulb given and do the following:

1. Explain the meaning of 75W, 240V and 12W, 240V.
2. Find out which of the bulbs costs more.
3. Find out which of the bulbs lasts longer.
4. Learners connect the bulbs to power source and observe brightness and feel the heat given out by each and record their findings.

Activity Five

Give the following activity to your students

The table below gives the appliance usage of households A and B

Household A	Household B
5 energy saver bulbs each 12W used 4hours a day	5 filament bulbs each 75W used 3hours a day

If the standard service charge is sh. 2000 per month, the cost of a unit is Shs. 426 and V.A.T is 18%.

1. Find the amount paid by each household at the end of the month.
2. Advise the household which spends more on electricity on how to minimise the cost.
3. Present your findings to the class.
4. Calculate the saving of household A in a year and suggest the investment that can be made out of the saving.
5. Mention other energy sources used in the household and discuss how they should be used economically.
6. Write an essay outlining the good and bad habits of electricity usage in the house.

Activity Six

1. State the advantages and disadvantages of parallel and series wiring.
2. Identify the three pins of a plug.
3. Wire the plug.
4. Mention and practice safety precautions.
5. Demonstrate the proper position of fuses and switches.
6. Calculate the cost of electrical energy.
7. Calculate the appropriate fuse rating for an appliance.
8. Mention ways of minimising energy wastage.

Activity Seven

Use the following teaching aids to carry out this activity

Teaching/learning aids

• Electric meter.
• Energy savers of different ratings.
• Filament bulbs.
• Electric flat irons.
• Radio/TV.
• Fridge.
• Telephone charger.
• Electric cooker.

Procedure

1. Divide the learners into groups of 5 to 10 members and give them the appliances in the table below then ask them to answer the following questions.

Appliance	Safety provision	Power rating	Speed of meter (very fast, fast, slow, very slow)	Deductions
Energy saver bulb
Filament bulb
Flat iron
Radio
Electric cooker
Electric kettle
Telephone charger

1. Identify and record the power rating of each appliance.
2. Identity any safety precaution provision on the appliance.
3. Connect each appliance in turn to the power source and make observations on the meter.

2. Give a chance to each group to present their findings to the class.

Follow up questions

1. (a) Discuss the factors that may lead to high energy consumption in the household.

(b) For each factor mentioned in (a) give ways of minimising the energy consumption.

2. Describe how each of the safety provisions identified reduces risks of using electricity in the household.

Website Links

http://en.wikipedia.org/wiki/Watt-hour

http://searchcio-midmarket.techtarget.com/sDefinition/0,,sid183_gci797759,00.html

SAMPLE SCHEME OF WORK

TEACHER’S NAME SUBJECT NO. OF LEARNERS

SCHOOL NAME CLASS

WEEK	PERIODS	TOPIC	SUBTOPIC	SPECIFIC OBJECTIVES	CONTENT	METHODOLOGY	TEACHING AIDS	COMMENT
	5	Electricity	Domestic electricity	The learner should be able to: Describe the advantages and disadvantages of series and parallel connections Mention and practice safety precautions when wiring a house Explain the necessity of earthing some electrical appliances Demonstrate the proper position of fuses and switches Calculate the appropriate rating of fuses Calculate the cost of electrical energy consumption using the kWh as the base unit State the advantages and disadvantages of different types of lamps	- Wiring a building - 3 pin plugs - Safety precautions - Cost of electrical energy – the kWh - Lamps (filament, fluorescent, discharge, energy savers)	Discussion Group work Demonstration	- Electric meter - Energy savers of different ratings - Filament bulbs - Electric flat irons - Radio/TV - Fridge - Telephone charger - Electric cooker - tester
	2	Electricity	Distribution of electrical energy	The learners should be able to: Explain how electrical energy is transmitted over long distances State advantages of transmitting power at high voltages	- The grid system for single phase - Advantages of high voltage transmission for long distances	Demonstration Discussion

SAMPLE LESSON PLAN

DATE	CLASS	SUBJECT	NO.OF STUDENTS	DURATION	TIME
…../…./…..	SENIOR FOUR	PHYSICS	40-80	80 MINS	8.00-9.20 am

TOPIC : Electricity

SUBP-TOPIC : Domestic electricity energy consumption

Objectives

By the end of this activity the learners should be able to:

1. Read an electricity bill and establish its authenticity, owner, and time frame.
2. Interpret the terms used in the bill correctly.
3. Calculate the payment arrived at in the bill correctly.
4. Read and interpret the rating written on an electrical appliance correctly.
5. Estimate the energy consumed by an electrical appliance in a given period of time.
6. Suggest ways of economical energy consumption in the home with the aim of reducing energy bills.

Method

Group Work

Teaching aids

• Copies of electricity energy bills.
• A 75W, 240V filament bulbs, an 18W, 240V energy saver bulbs, a 40W, 240V fluorescent tubes, a 1600W, 240V flat irons, a 2KW, 240V kettles.

Time	Content	Teacher’s activity	Students’ activity
5min	Review calculation of electrical power and energy. P = v2/R= VI = I2R Energy = Power x time	Asks students to define electrical power and energy in terms of electrical quantities	Define electrical power and energy in terms of electrical quantities.
5min	The kilowatt hour. Definition The kilowatt hour is the energy consumed by a device of power 1000Watts in 1hour.	Guides students to define the Kilowatt hour as the electricity board unit.	Define the Kilowatt hour.
15min	The energy bill Features of an energy bill: Authenticity The owner The time frame Meter readings Stages of arriving at the bill	Organises students into groups of 5-10 learners. Gives the students the electricity bill copies Asks them to study the bill and describe its features.	Get into groups Receive bill Study the bill and describe its features
10min	Comparison of the energy saver and the filament bulb.	Gives the groups one filament bulb of 75W, 240V and one energy saver bulb of 12W, 240V. Instructs the different groups to explain the meaning of the ratings.	Explain the meaning of 75W, 240V and 12W, 240V. Explain the meaning of the rating.
10min	Differences between the two bulbs. The 12W energy saver gives more light and less heat. The filament bulb gives out less light but a lot of heat. The energy saver is more efficient in lighting and durable although more expensive.	Instructs students to discuss observations made on the bulbs when they working. Listens to the students as they discuss the cost and durability of each of the bulbs	Discuss their observations.
10min	Energy consumed by an appliance and the cost	Asks students to find the difference in the cost of electricity which a house using 5 filament bulbs for 4 hours a day for a month, compared to a house which uses 5 energy saver bulbs for 3 hours a day. Explains to the learners the meaning of: V.A.T and service fee.	Calculate the total energy and the total cost in each case and find the difference in the bills. Listen
20min	Electrical appliances in the home	Instructs learners to present their group findings to the rest of the class and guides in summarising	Each group presents to the rest of the class
5 min	Home work	Gives the learners an assignment	Take note of the assignment.

Lesson Evaluation

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Propagation

Subject: Physics

Class: S1

Topic: Behaviour of light

Sub-topic: Propagation

Introduction:

This topic describes the behavior of light as it travels through a medium of uniform density, and when an opaque object is placed in its path. This leads to the formation of shadows and eclipses.

Knowledge of this aspect of light is applied in many situations of life, e.g. photography, security systems, driving mirrors, vision, eyeglasses, binoculars, etc.

Brief description of topic:

This unit describes the behaviour of light in a homogeneous medium and when an opaque object obstructs it. Knowledge of the rectilinear propagation of light would enable the learner to explain the occurrence of shadows, and eclipses. The learner is expected to use locally available materials to construct a pinhole camera and explain how it works.

Content: Definition of light, sources of light, speed of light, types of media, rectilinear

Propagation, rays and beams, eclipse and the pin-hole camera.

Teaching /l earning materials

Light bulbs of different sizes, opaque objects,

Cardboards with holes, flexible tube.

Methodology

Discussion, experimentation, group work.

Teacher’s guide

(A) Learning objectives, learners should be able to:

1. Demonstrate experimentally the rectilinear propagation of light.
2. Explain the formation of shadows and eclipses
3. Construct and describe the working of a pin-hole camera

(B) Teacher’s notes

• Light is a form of energy (ask learners to give different uses of light)
• Sources of light include; artificial e.g. light bulbs, fires, moon. and Natural e.g. sun, light flies.

Types of materials

• Opaque – don’t allow light to pass through them.
• Transparent – allow little light to pass through them
• Translucent – allow little light to pass through them e.g. frosted glass.

[Allow learners to give examples of their own]

The speed of light in air is approximately 300000000ms-¹, learners should express this in standard form and in km/h.

Teacher performs experiment of show the rectilinear propagation of light using (a) cardboards and (b) a flexible tube.

Rays are paths of light; beams are a collection of rays, parallel beams, convergent beams, and divergent beams.

(C) Experiments to show the rectilinear propagation of light.

Method 1

1. Begin with the holes out of line and ask some few students to observe at E and tell class about their observations.
2. Using a string through the holes to ensure they are in a straight line and repeat procedure (i) above then let the learners draw the conclusion.

Method 2

With the tube in various configurations keep on asking the question ‘can you see the light? The observation leading to the right conclusion will come at the end.

Shadows

Formation of shadows with sharp boundaries is evidence that light travels in a straight line.

Experiments to study how shadows are formed.

1. Small source with a large obstacle

2. Large source with large obstacle

3. Large source with a small obstacle.

ECLIPSES

During an eclipse, the sun, earth and moon are in a straight line. The word eclipse means hiding.

Eclipse of the sun

• The moon lies between the sun and earth

Eclipse of the moon

The earth lies between the sun and moon the earth casts a shadow on the moon.

The teacher should assemble a pin-hole camera and explain how it works in class.

A pin-hole camera

Tasks with the pin-hole camera

Tasks answers

(a) Describe the image	(a) The image is real, inverted
(b) In what ways can the image be magnified?	(b) Decreasing object distance or Decreasing the length of the camera.
(c) What is the effect of enlarging the pin-hole?	(c) The image becomes brighter and blurred (i.e. without sharp boundaries).
(d) Explain your observation in (c) above	(d) A large hole may be considered as consisting of many pin-holes each one producing its own image. When several images overlap, a blurred image is obtained - An enlarged hole allows more light to pass making the image brighter.

EXERCISE

1. What is light?
2. List

1. 2 natural sources of light
2. 2 artificial sources of light

3. Mention three uses of light
4. The speed of light is 300000000ms-¹

Express this in

1. Standard form
2. Km/s

5. Using a labelled diagram describe an experiment to show that light travels in a straight line.
6. Define the following; (a) rays (b) beam

7. Copy and complete the following

8. During an eclipse of the moon the
   1. Earth lies between the moon and sun
   2. The sun lies between the earth and moon
   3. The moon lies between the sun and earth
   4. The earth, sun and moon are not lying I a straight line

9. In a pin-hole camera what is the effect of
   1. increase the length of the camera
   2. increasing the object distance
   3. increasing the size of the pin-hole

Explain your answer in (c) above

10. A tree 15m tall is viewed using a pin hole camera 30cm long. The distance of the tree from the camera is 90m.
    1. Describe the appearance of the image
    2. Calculate the size and magnification of the image.

ANSWERS:

1. Light is a form of energy

2. (i) Natural sources of light-sun, fireflies

(ii) Artificial sources of Light-electricity bulb, fireplace

3. (i) enable us to see

(ii) Used in photography

(iii) Used by solar cells

4. (i) 3 x 10 ms-¹

(ii) 300,000 km s-¹

5. [See experiment]

6. (a) Ray –direction or path taken by light

2. Beam – a collection of rays

7.

(ii) convergent beam

(iii) Parallel beam

8. A

9. (a) image is enlarged

(b) image is diminished

(c) Image becomes brighter and blurred

Explanation of (c)

• Larger hole allows more light pass .a large hole acts as a collection of pin-holes each one producing its own image. when all the images overlap, blurred image (without sharp boundaries is obtained.

10) a) the image is real, inverted and diminished.

b) x/10 = 0.3/90

x = 0.033m

Or 3.3cm

Magnification = 0.033/90 = 0.0004

SCHEME OF WORK

School ……class……. Teacher……..term…….year……

Periods	Topic	Sub-topic	Objectives	Content	Methodology	T/L Aids	Ref	Remarks
4	behaviour of light	Propagation of light	By the end of lesson the learner demonstrates the rectilinear propagation of light, -Explains the formation of eclipses	- Definition of light, sources of light. Speed of light, Rectilinear Propagation Rays and beams Eclipses	Discussion Experimentation	Bulbs Cardboards Flexible tube	New complete junior physics by A. Atkinson And H.sinuff Pg 156 ()
2	Behaviour of light	Propagation of light	Constructs and explains the working of a pin hole- camera	Pin hole camera	Group work Experiment	Cardboards Glue Tracing paper Razor blades	New complete junior physics by A. Atkinson And H.sinuff Pg 160

LESSON PLAN:

SUBJECT: PHYSICS

CLASS: S1

TOPIC: Behaviour of light

SUBTOPIC: propagation of light

Time: 80 minutes

Objectives: by the end of the lesson the learners should be able to:

Demonstrate experimentally the rectilinear propagation of light.

Teaching aids: candle, cardboards, flexible tube, string, lighter.

Method: Discussion, experimentation

Reference: New complete junior physics by Atkinson and H.sinuff, pg 156.

Time	Teacher’s activity	Pupil’s activity
20min	-Ask pupils to define light, to mention sources of light and categorize them. -Discusses the speed of light and writes it on blackboard, asks pupils to express it in km/s and in standard form. - Ask pupils the uses of light - Discuss transparent, opaque and translucent materials and ask pupils to give examples.	Attempt to reply and should give the correct response as: -Light is a form of energy, place sources of light in categories of natural and artificial sources. - Discuss speed of light with teacher - Convert speed of light to km/s and also in standard form. Give uses of light -Mention examples types of media.
25min	Teacher sets up the following experiment Begins with the holes out of line and ask a few pupils to observe, then arranges the holes in a straight line and the same pupils repeat the observation. - The teacher then asks the pupils for their deduction. -Teacher reinforces the conclusion by repeating experiment using a flexible tube.	- Observe and draw deductions.
15min	Defines a ray, beam Defines parallel, convergent and divergent beams and asks pupils to mention examples.	Give examples
15min	Give exercise and supervises (see exercise)	Do exercise

REFERENCES:

Atkinson. A and Sinuff. H New complete Junior physics (1983) Longman, Nairobi.

Light I

Unit: 5

Subject: Physics

Class: S.1

Topic: Behaviour of Light.

Sub-topic: Reflection of light from plane surfaces.

Introduction:

At home we use mirrors in our wardrobes and bathrooms. We often carry them in our hand bags, plane mirrors have many uses in our daily lives. We can use either one mirror or a combination of mirrors to make useful and interesting devices. Children like playing with mirrors. They see their images in them but can’t touch them.

Time: Min: 200minutes. Maximum 240minutes.

Brief description of subtopic.

This subtopic explores the properties of images obtained using a single plane mirror and a combination of plane mirrors. The laws of reflection are used to provide an explanation for the observations made. Equipped with these principles one is able to devise optical devices using a plane mirror or a combination of plane mirrors.

Content: Laws of reflection, regular and irregular reflection, properties of images in plane mirrors, simple periscope, mirrors inclined to each other, the kaleidoscope.

Learning objectives: learners should be able to;

1. State the laws of reflection.
2. Experimentally verify the laws of reflection.
3. Describe the images formed by plane mirrors.
4. Construct a simple periscope and kaleidoscope.

Teacher’s Notes.

Reflection in Plane Mirrors

AO = Incident ray

OB = Reflected ray

ON = normal to mirror

i = angle of incidence

r = angle of reflection.

Laws of reflection:

1. The incident ray, reflected ray and normal to surface at the point of incidence all lie in the same plane.
2. The angle of incidence is equal to the angle of reflection.

Regular reflection Irregular (Diffuse) reflection.

- Abeam of light reflected from a shiny smooth surface is very bright. This makes it difficult to recognize details of the reflecting surface.

- Light is reflected irregularly (diffusely) from most objects around us. This enables us to see and recognise detail on the reflecting objects.

Properties of images in plane mirrors, they are;

1. Upright (i.e. the same way up as the object)
2. Virtual (i.e. cannot form on a screen)
3. Same size as object
4. Laterally inverted (i.e. the left of the object looks to be the right of the image)
5. Distance of the object from the mirror is equal to the distance of the image from the mirror.
6. A line joining a point on the object to its reflection on the image is perpendicular to the mirror.

Formation of an image in a plane mirror – How the eye sees the image.

An observer views an object when rays of light from the object are reflected from the mirror to the eye (s) of the observer.

• Draw ray OB
• Construct a normal at B
• Draw the reflected ray BD, use a protractor to ensure i and r are equal.
• Extrapolate DB behind the mirror.
• Repeat the procedure with another ray OC.
• The two extrapolated rays meet at 1 where the image appears to be.
• Join O to 1
• Measure OA and A1, what do you find? Answer OA = A1
• Measure the angle between O1 and the mirror. Answer angle = 90⁰

EXPERIMENTS:

Experiment to verify the laws of reflection.

(a) Using no-parallax method.

Apparatus: soft board, optical pins, plane mirror, protractor and a plane sheet of

paper.

Procedure:

1. Draw a line to mark the silvered surface of the mirror on the sheet of paper.
2. Mark a point X on the line.
3. Draw a normal at X.
4. Using a protractor mark off an angle ray of incidence, e.g. 20⁰ and draw the incident.
5. Stand the mirror vertically on the line representing the silvered surface.

6. Tuck pins P₁ and P₂ in the incident ray.

Note: P₁ and P₂ should stand vertically and far a part.

7. Position your eye at E to view the reflections of P₁ and P_2.
8. Tuck in P₃ such that P₁, P₂, and P₃ appear to be in a straight line.

Move your eye side ways to ensure there is no relative movement (no-parallax) between P_{1 ,}P_{2 and} P3 .

9. Repeat procedure (ix) above with another pin P₄.
10. Join P₃ and P₄. It should cross the silvered line at X.
11. Measure the angle of reflection, r.

Repeat procedures (iv) to (xii) for angles I = 30⁰, 40⁰, 50⁰, 60⁰, 70⁰

Tabulate your results in the table below.

i0	r0
20 30 40 50 60 70

What do you observe? (Generally, the angle of incidence is equal to the angle of reflection)

(b) Using a ray of light.

Apparatus: plane mirror, protractor, empty tin with a narrow slit, Bulb,

Cell holder, Cells, connecting wires.

[Hint: this experiment is best done in a dark room.]

1. Draw a line to represent the silvered surface.
2. Using a protractor construct a normal at X.
3. Position the protractor in such a way that the centre of the protractor is at X.
4. Direct a ray of light at X.
5. Read i and r.
6. Repeat procedures (iv) and (v) for various angles of incidence each time noting the angle of reflection.
7. Tabulate your results in the table below

i0	r0

What do you notice? Answer: The angle of incidence is equal to the angle of reflection.

3. To count the number of images in two mirrors inclined to each other.

1. Arrange two plane mirrors at right angles to each other and stand a small object between them.
2. Count the number of images.
3. Repeat procedures (i) and (ii) for angles of 120⁰, 100⁰, 80⁰, 60⁰, 50⁰, 40⁰, and fill your results in the table below:

Angle	Number of images.
1200 1000 800 600 500 400

Question: How many images will be visible when the angle is 110⁰, 70⁰, 30⁰, 20⁰, 10⁰, and 5⁰ and x⁰?

Answer 2, 4, 35, 71 and 360 - 1

Respectively.

Explanation:

Consider 2 plane mirrors inclined to each other at 60⁰.

M₁ is the reflection of M₁ in M₂

M₂ is the reflection of M₂ in M₁

M₂ and M₁ also act as mirrors.

M₁ is the reflection of M₁ in M₂.

M₂ is the reflection of M₂ in M₁.

These two also act as mirrors.

The combination of mirrors produces images A, B, C, D, and E.

In the diagram above you can count six sectors i.e. 360⁰ = 6 and 5 images.

60⁰

Therefore the number of images is given by:

Number of images = 360⁰ - 1

Angle between mirrors.

ANNULAR ECLIPSE

There are times when the distance of the moon from the earth is such that the tip of the umbra fails to reach the earth’s surface. From the earth, the sun appears as a circular ring. This is called annular eclipse.

Object The Kaleidoscope.

• Cut several discs of wood.
• Using a protractor mark out shaded sector AOB, with angle AOB = 30⁰
• Carefully cut out the shaded sector.
• Using wood glue fix plane mirrors along OA and OB.
• Repeat the procedure by changing the angle to 20⁰, 40⁰ 50⁰, 60⁰, 90⁰, 120⁰ using cardboard.
• Place one of the discs you made above at the bottom of the tube.
• You can now drop flowers or other small coloured objects into the tube.

For each one you drop into the tube, apparently many others are “produced”. Using discs with mirrors at different angles can enjoy this effect.

Parallel mirrors.

Now position the mirrors parallel to each other and count the number of images. How many can you get? Answer: very many (infinity)

Illustration.

I₁ = reflection of O in mirror 1

I _{1 2} = Reflection in Mirror 1 followed by reflection in mirror 2.

I _{1 2 1} = Reflection in mirror 1 followed by reflection in mirror 2, followed by reflection in mirror 1.

e.t.c

Question: mention one practical application of parallel mirrors.

Answer: in saloons customers are able to view both the front and back of their heads.

Project: construction of a simple periscope.

Materials: 2 plane mirrors,

Cardboard paper,

Glue,

Protractor.

Procedure: -

- Using glue and cardboard, construct 3 tubular sections each about 50cm long.

- Ensure that the edges of the tube are normal to each other.

- Using glue fix two plane mirrors in the tubes as in diagram.

- Make sure the mirrors each make angle of 45⁰ with the sides of the tube.

- Now join the tubes and fix them firmly.

Note: the periscope will not work properly if the mirrors are not parallel to each other.

You can now use your periscope to view different scenes.

- Describe the image you see.

- Mention some uses to which your periscope can be put.

[Answer (i) people at the back of crowd may use periscopes to see over the heads of people in front of them.

(ii) Sailors in submarine water often use them to see objects on the surface.

(iii) Can be used to view objects around edges of building.]

Diagram showing how a periscope works.

Mirror 1 forms image I₁

Mirror 2 views I₁ and forms image I₂

The observer sees I_2.

To draw this diagram accurately you should note the following:

1. The two mirrors must be parallel to each other.
2. A line joining I, O, I₂ is perpendicular both mirrors.
3. OI = OI₂
4. You can now use the positions of I₁ and I₂ to complete the diagram.

EXERCISE.

1. State the laws of reflection.
2. (i) Distinguish between regular and irregular reflection.

2. Fill in the table below.-

	Regular	Irregular.
Advantage
Disadvantage

3 (i) plane mirror.

Copy the diagram above and show the image.

(ii)

A girl run towards a plane mirror in the direction shown. Copy the diagram show the direction of the image.

4. A plane mirror is hanging on a vertical wall; a boy 1.6m tall wants to see both his feet and top of his head in the mirror when he is standing erect.

Assuming his eyes are 15cm below the top of his head find

1. The minimum height of the mirror.
2. Its distance from the floor.

5.

In the diagram above two pupils A and B stands behind B along a straight line joining AB to the mirror, if AB is perpendicular to the mirror, Find the distance between B and the image of A.

Answers.

1. The incident ray, reflected ray and normal to surface at point of reflection lie on the

same surface.

The angle of incidence is equal to the angle of reflection.

2. (i) Regular reflection: This is when a parallel beam is incident on a regular surface

producing a parallel-reflected beam.

Irregular reflection: This is when a parallel beam is incident on an irregular surface

producing a non-parallel reflected beam.

(ii)

	Regular	Irregular.
Advantage	Produces a bright beam of reflected light.	Enables us to recognise details on the reflecting surface.
Disadvantage	The reflected beam is very bright. It is difficult to recognise detail on the reflecting surface.	The reflected beam is dull.

3 (i)

(ii)

4.

Length of mirror required = AB

AB = 0.725 + 0.075 = 0.8m

Distance from the floor = 0.725m.

5. Diagram.

SCHEME OF WORK

School…… Class: S.1 Term……… Year…………….

Subject Physics.

Week ending on.	Periods	Topic	Sub-topic	Objectives	Content	Methodology	T/L Aids	Reference	Comment.
	2	Behaviour of light.	Reflection of light from plane surfaces.	By the end of the lesson, the learner; - States the laws of reflection. - Describes images in plane mirrors. - Draws a ray diagram to show how the eye sees the image.	Laws of reflection Regular and diffuse reflection. Properties of images. Formation of an image (How the eye sees the image).	Discussion	-Plane mirrors -Protractor - Rulers	New complete Junior Physics,by A.Atkinson and H.Sinuff . Ordinary level physics by A.F. Abbott.
	3	Behaviour of light.	Reflection of light from plane surfaces.	Experimentally - Verifies the laws of reflection. - counts the number of images in mirrors inclined to each other. - Draws a ray diagram to show how a periscope works.	Experiments - To verify the laws of reflection. - To count number of images in mirrors inclined to each other. - The kaleidoscope - The periscope	- Class experiments - Project	- Plane mirrors. - Optical - Pins - Protractors - Tin with slit. - Bulb, bulb holder. - Cells, cell holder. -Connecting wires. - Soft board.	- - do --	The theory of the Kaleidoscope and periscope should be done in class. The learners should construct them as projects outside class.

LESSON PLAN.

Subject: Physics

Topic: Behaviour of light.

Sub Topic: Reflection of light from a plane mirror.

Time: 80mins

Objectives;

By the end of the lesson the learner should be able to:

1. State the laws of reflection.
2. Describe the image formed in a plane mirror.
3. Draw a ray diagram to show how the eye sees the image.

Teaching aids: Plane mirrors, protractor Rulers.

Method: Discussion.

Reference: - New complete Junior physics by A. Atkinson and H. Sinuff.

• Ordinary level physics by A.F Abbott.

Time	Content	Teacher’s Activity	Pupils Activity
5min	Review	Teachers review lesson on propagation of light by asking questions on.	Answer questions asked.
10min	Definition of reflection. Laws of reflection properties of images.	Teacher asks leading questions to lead pupils into defining reflection and writes down correct answers on chalkboard. Teacher draws the diagram on reflection on black board And defines terminology and explains the laws of reflection. The teacher distributes some mirrors and ask pupils to state the properties of images as he writes the correct ones on black board.	Try to define reflection. Copy definition of reflection. Copy diagram in exercise books and the accompanying terminology and the laws of reflection. State the properties of images and copy them.
20min	How the eye sees the image.	Using a black board ruler and protractor accurately draws the diagram. On how the eye sees the image carefully explaining each of the steps necessary to produce an accurate diagram. Teacher goes round class supervising. Writes on blackboard accompanying notes.	Copy diagram in exercise books. Copy the notes.
5min		Summarises the lesson by asking leading questions.	Answer questions
Self evaluation: