FORM 5 CHAPTER 2: ELECTRICITY

2.1 Electric fields and charge flow [ ……./ 25 x 100 = …………..%]

A student is able to : describe an electric field. sketch electric field lines showing the direction of the field. state the relationship between electric charge and electric current. define an electric current

1. An electric field exists in the space surrounding a (1)……………….. body.

2. Draw the patterns of electric field lines of the charges below:

(a) (2) (b) (3)

(b) (4) (d) (5)

3. Like charges (6) …………… each other , unlike charges (7) ……………… each other.

4. An electric current is defined as (8) ……………………………………………..

Electric current, , (Q measured in (9) ………………..

5. Electric current is measured with an (10) ……………… in SI unit (11) ……………

1

Exercise

2

1. A charge of 30 coulombs flows through a bulb in1 minute. What is the current flowing in the bulb?

(12)

2. A car battery can supply a current of 4A for 5s. What is the amount of charge stored in the battery?

(13)

3. A current of 2.0A flows through a lamp. How long does it take for

1000 C of charges to flow through the lamp?

4. A fuse wire will burn if a current of 13A flows through it for 100ms. Determine(a) the quantity of charge that

flows through the fuse wire.

(15)

(b) the number of electrons that flow through the fuse wire if the charge on 1 electron is 1.6x10-19C.

(16)

3

(14)

5. Draw the symbols of these electrical items.

ammeter (17)Cells (21)

voltmeter (18) Switch : open

: closed

(22)

connecting wire (19)(23)

resistor(20)

bulb(24)

rheostat(25)

2.2 The relationship between electric current and potential difference

[ ……./30 x 100 = ……….% ]

A student is able to :

define potential difference. describe the relationship between current and potential difference. state Ohm’s Law define resistance explain factors that affect resistance solve problems involving potential difference, current and resistance.

1. The (1) …………………………………….,V., between two points in a circuit is defined as the (2) ……………..…,W in moving (3) …………………of charge from one point to the other point. It is measured with a (4) ……………………. in SI unit (5)………………………….

2. Sketch a graph to show the relationship between potential difference ,V and current, I for a resistor that obeys Ohm’s law.

4

(6)3. State the Ohm’s law.

Ohm’s law state that the (7) …………… that passes through an ohmic

conductor is (8) ……………………………………………………………….. to the

(9) …………………………………………applied across it if the (10) …………….. and other physical conditions are constant.

By Ohm’s law, V I ,

= constant [ known to be the resistance,R ]

4. The (11) …………………………..of a conductor is defined as the ratio of the potential difference,V, across the conductor to the current, I, flowing through the conductor.

R =

5. In the table below, write down the relevant hypothesis for each of the experiments to investigate the factors affecting the resistance, R of the conductor.

Factors Diagram Hypothesis Graph

Leng

th o

f th

e co

ndu

ctor

, l

The resistance,R is(12) …………………………… to the length of the conductor

The

cro

ss-

sect

iona

l are

a of

th

e co

ndu

cto

r, A The resistance,R is

(13) …………………………. to the cross-sectional area of the conductor

5

The

typ

e of

m

ater

ial o

f th

e co

ndu

ctor

Different conductors with the same physical conditions have different resistance

The

tem

pera

ture

of

the

cond

ucto

r

The higher the temperature of the conductor, the higher the (14) ………………………

6. What are the factors affecting the resistance of a conductor?

a) (15) …………………………………………....................

b) (16) ……………………………………………………….

c) (17) ……………………………………………………….

d) (18) ………………………………………………………..

Exercise

1. In the diagrams below, determine the values for V, I and R.

(a) (b)

I= ………… (19) R=…………. (22)

R= ……. … (20) V=………….. (23)

V= I = =

A1.5A

V=?

6Ω

AI=?

9V

6Ω

6

= (21)

(24)

(c) (d)

I= .............. (25) R= ............ (28)

V= ............. (26) V=............. (29)

R= I =

(27) (30)

2.3 Series and parallel circuits [ ………./ 35 x 100 % = ……….]

A students is able to :

identify series and parallel circuits. compare the current and potential difference of series circuits and parallel circuits. determine the effective resistance of resistors connected in series. determine the effective resistance of resistors connected in parallel. solve problems involving current, potential difference and resistance in series circuit, parallel circuits and their combinations.

1. Match the circuits below

(1)

A3mA

12V

R=?

AI=?

240V

2kΩ

Parallel circuit

7

(2)

2.

Series circuit Parallel circuit1. 1.

2. 2.

3. 3.

4. Has only (3) ……. path for the current to flow.

4. Has (4) ………………… path for the current to flow

5. The current is the (5) ………. throughout the circuit.

5. The current is different at (6) …………… Points in the circuit.

6. The component with the largest resistance has the (7) ……………… potential difference across it.

6. The potential different across all the components is the (8) ……………

7. (9) …………….. flows when the switch is open.

7. No current flows only in the branch that is open. Current (10) …………… to flow in other branches that are closed.

3. Determine the total effective resistance between point X and Y.

Answer

R= = (11)

Answer(b)

Answer(c)

(13)

Series circuit

8

(12)

Answer (14)

Answer

(15)

Answer

(16)

9

Answer

(17)

Answer

10

(18)4. In the circuits below, determine the reading of the ammeter marked by ‘?’

(a) ……. (19) (b) ……… (20)

(b)

(b)

(b)

(b)

(b)

(b) ……. (21) (d) ……….. (22)

Finally

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(e) ………….. (23)

(f) …………… (24)

(g) ……………. (25)

(h) …………….. (26)

5. In the circuits below, determine the reading of the voltmeter marked by ‘?’

(a) (b) (c) (27) (28) (29)

(d) (e) (f) (30) (31) (32)

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6. A 8Ω resistor and a 12Ω resistor are connected in series. The current in the 8Ω resistor is 1.5A and the potential difference across it is 12V. What is the current and the potential difference across the 12Ω resistance?

I = (33)V =

= = (34)

7. When two identical resistors are connected in parallel, the effective resistance is 3Ω. What is the effective resistance if the two resistors are connected in series?

(35)2.4 Electromotive force and internal resistance [ ……../ 15 x 1000 = ………%]

A student is able to :

Define electromotive force (e.m.f.). Explain internal resistance. Determine e.m.f. and internal resistance. Solve problems involving e.m.f. and internal resistance

1. The electromotive force (e.m.f.) is defined as the (1) ………………… by a source

in driving (2) ……………………….. of charge through a complete circuit.

2. The internal resistance, r of a cell is due to the opposing flows of (3) ……………..

in the electrolyte within the electrodes in a closed circuit.

3. Calculate the e.m.f of the following sources in the diagram below.

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Answer E=

= (4)

Answer E= =

(5)

Answer E=

(6)

Answer

E=

=(7)

4.

The equation for the graph above is given by :

V = -r I + E

From the V-I graph show how you determine the value of

V= potential differencer= internal resistanceE= e.m.f. of cellI = Current

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(a) e.m.f, E

(8) …………………

(9) …………………

(b) internal resistance, r.

(10) (11)

5. A dry cell has an electromotive force, e.m.f. of 3.0 V and internal resistance, r of 0.5 Ω is connected in series with a resistor, R Ω. If a current of 0.4 A flows through the circuit, calculate(a) the potential difference across the resistor R

(12)(b) resistance R

(13)

6. A dry cell with an internal resistance of 2.0Ω is connected to a bulb. The potential difference across the bulb is 2.4V when the current flow is 0.3A. Determine the e.m.f of the dry cell.

(14)

7. A cell of e.m.f 12V and internal resistance r Ω is connected to a bulb with resistance 2Ω . The current in the circuit is 5A. What is the internal resistance of the cell?

15

(15)

2.5 Electrical energy and power [ ………/ 16 x 100 = …………%] A student is able to :

Define electrical energy Define electric power Solve problems involving electrical energy and power

1. (1) …………………………., E, is released when electric charges flow through any two points in an electric circuit.

2. One joule of electrical energy is released when (1) ………………………. of electric charge flows through a potential difference of (3) …………. Electrical energy, E, is measured in (4) …………………….

Electrical energy, E = V, potential difference Q, number of charges

E = (5) = (6)

3. (7) ........................is defined as the rate of energy dissipated by a resistor.

SI unit for power is(8) .............................

Hence, Power = ________________(9)

16

time taken

= V I

4. Efficiency = energy output X 100%

energy input

= ___________ x 100% (10)

Exercise

1. A toy car is operated with a battery of voltage 3.0V and the current flow is 7.0A. Find :

(i) the power delivered to the motor (ii) energy dissipated in the motor in 6.5 minutes of operation.

(i) P = =

= (11)

(ii) E= =

= = (12)

2. A 40W fluorescent lamp transfer 60% of the electrical energy to light energy. How much light energy does it emit in two minutes.

E= = = (13)

3. An electric kettle with a power of 2kW is used for 10 minutes, three times a day. If the cost of electricity is 25 cent per unit, what is the cost of operating the kettle for 30 days?

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(14)

7. A motor which is connected to a 120V DC voltage source produces 320W of mechanical power. The current from the voltage source is 3.0A.

(a) what is the input power of the motor?

Input power, P = = =

(15)

(b) what is the motor’s efficiency? (16)

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