Electricity Exercises 1

Name: ______________________________________ (

) Class: _____ Date: ________

Electricity Exercises 1.

Which of the following statements is/are correct about the circuit above? (1)

Electrons flow from right to left through the bulb A.

(2)

Charges will be used up when the bulbs glow.

(3)

Current will flow slower in bulb B than in bulb A.

A)

(1) only

B)

(3) only

C)

(1) and (3) only

D)

(1), (2) and (3)

2. If the electron flow rate through a resistor is 3.76 x 1018 each second, what is the current passing the resistor? (Given: Charge of an electron = -1.6 x 10

A

A)

0.6 A

B)

2A

C)

1.88 x 1018 A

D)

6.25 x 1019 A

-19

C)

3. In the following circuit, if the p.d. (voltage) across bulb A is 3 V and the p.d. voltage across bulb B is 2 V.

Which of the following statements is/are correct? (1)

The charge flow rate through bulb A is higher than that

through bulb B. (2)

Bulb A consumes 1 J of energy more than bulb B, for each

coulomb of charge. (3)

The current flowing in the bulb A is 5 A.

A)

(1) only

B)

(2) only

C)

(1) and (2) only

D)

(1), (2) and (3)

4. The e.m.f. of which of the following batteries is different from the others? A)

B)

C)

D)

5. Which of the following is the correct connecting of a voltmeter for measuring voltage across a resistor? A)

B)

C)

D)

6. Which of the following CANNOT increase the resistance of a copper wire? (1)

Wind the wire into coils.

(2)

Put the wire into the flame of a Bunsen burner.

(3)

Stretch the wire, and plus decrease it radius.

A)

(1) only

B)

(1) and (3) only

C)

(2) and (3) only

D)

None of the above

7. The relation of the current passing through a conducting wire changes with the voltage across is shown in the figure below. If the temperature of the wire does not change when current passes the wire.

Which of the following statements is/are correct? (1)

The conducting wire does not obey Ohm's law.

(2)

The resistance of the conducting wire increases with the

voltage across it. (3)

The resistance of the wire is zero when there is no current

passes through it. A)

(1) only

B)

(2) only

C)

(1) and (2) only

D) (2) and (3) only

8. A conducting wire of length l and diameter d has resistance of 10 Ω. If a same kind of conducting wire is 2l in length and 0.5d in diameter, then what is its resistance? A)

5 Ω

B)

10 Ω

C)

40 Ω

D)

80 Ω

9. The resistance-temperature graph of the following circuit is shown below.

When the current passes through the metal wire is 1 A, the temperature of the wire is 25 oC. What is the current passes through the metal wire when the temperature of the wire is 200 oC? A) 0.417 A B) 0.6 A C) 1 A D) 1.5 A A

10. In the following figure, if switch K is closed, then

(1)

The voltmeter reading increases.

(2)

The ammeter reading increases.

(3)

Bulb N becomes brighter.

A)

(1) and (2) only

B)

(1) and (3) only

C)

(2) and (3) only

D)

(1), (2) and (3)

11. Current of I amperes passes through a bulb for t minutes. How much charge has passed through the bulb? A)

It C

B)

60It C

C)

I C 60t

D)

t C I

12. Energy of 12 J is supplied when 6 C of positive charges pass through a supply. What is the e.m.f. of the supply? A) 2 V B) 12 V C) 24 V D) 12 J

13. If each resistor in the following circuit is with resistance R,

What is the total resistance across PQ?

A)

4 R 3

B)

2R

8 R 3

C) D)

6R

14. In the following circuit, the e.m.f. of the battery is V and the resistance of each resistor is R.

What are the readings of voltmeter and ammeter?

A) B) C) D)

Reading of ammeter VR

V R V 2R 2V R

Reading of voltmeter

V 2 R 2 V 2 R 2

15. If each resistor in the following circuit is with resistance R.

Which of the following is INCORRECT? A) The reading of A1 = A6. B) The reading of A2 = A3. C) The reading of A2 = A5. D) The reading of A3 = A4. 16. If each resistor in the following circuit is with resistance R. When the switch S is closed, then

A) B) C) D)

Reading of A1 Increases Decreases Increases Decreases

Reading of A2 Decreases Increases Increases Decreases

17. A student wants to measure the resistance of a resistor, and it is known that the resistance is less than 10 ohms. Which circuit should be used? A)

B)

C)

D)

18. In the following circuit, the resistance of R2 is half of that of R1. When S1 is closed, the ammeter reads 1.6 A.

What is the reading of the ammeter when both S1 and S2 are closed? A) 0. 6 A B) 2.8 A C) 3.6 A D) 4.2 A

19. Four identical bulbs are connected as following circuit.

Which of the following statements is/are correct? (1) Lamp W and X glow with equal brightness. (2) Lamp Y and Z glow with equal brightness. (3) Lamp Y is brighter than lamp W. A) (1) and (2) only B) (2) and (3) only C) (1) and (3) only D) (1), (2) and (3)

20. In the following circuit, the voltage across the battery is 2V. If the resistance of of R1 = A,R2 = 2A, R3 = 3A and R4 = 4A, then what is the voltage across R3?

A)

V 3

B)

3V 10

C)

6V 31

D)

12V 31

21. In the following circuit, the voltage of the cell is 1 V, and the three resistors are identical, each having a resistance of 1 i .

What is the reading of the ammeter in the circuit? A) 0.5 A B) 1 A C) 2 A D) 3 A

22. In the following figure, the ratio of the resistance of R1 to that of R2 to that of R3 is 1 : 2 : 3.

What is the ratio of the current passing through R1, R2 and R3? A) 1 : 2 : 3 B) 3 : 2 : 1 C) 5 : 1 : 1 D) 5 : 3 : 1

Directions: Each question below consists of two statements. Decide whether each of the two statements is true or false. If both are true, then decide whether or not the second statement is a correct explanation of the first statement. Then select option A, B, C or D, according to the following table.

A

1st statement True

B

True

C

True

D

False

2nd statement The 2nd statement is a correct explanation True of the 1st statement. The 2nd statement is NOT a correct True explanation of the 1st statement. False True

1. 1st statement The brightness of a bulb with fixed resistance depends only on the p.d. across it.

2nd statement The larger p.d. across the bulb, the more the energy is given to the bulb by each coulomb of charge.

The resistance of a metal wire increases with its temperature.

The metal wire does not follow Ohm's law.

2.

3. When a resistor is added to a circuit, Equivalent resistance of a circuit increases if resistors are connected in total current flowing in the circuit must be decrease. series. 4. When some resistors are connected to a battery, as compared with a parallel circuit, the battery can last longer if resistors are connected in series.

Less current is drawn from the battery when resistors are connected in series.

If bulbs connected in series, the current passing them is different.

Energy is given to the bulbs when current passes them.

5.

7. When a voltmeter is connected across a resistor of small resistance, there would be little current passes through it.

Voltmeter has a very high resistance.

Birds can stand on an overhead highvoltage cable without getting electric shock.

Overhead high-voltage cables are insulated by plastic coatings.

8.

Short questions

1. The following diagram shows a labeled '15 Ω, 8 A' rheostat (variable resistor) connected by wires.

(a)

What is the meaning of '15 Ω' on the label. (1 mark)

(b)

To obtain the maximum equivalent resistance across X

and Y, the sliding contact of the rheostat should be placed at the middle of the coil. Explain why and also calculate the maximum equivalent resistance across X and Y. (4 marks)

2. The following figure shows a simplified car wiring diagram. left headlight

right headlight

left sidelight

right headlight

battery

S1 S2

dashboard light

car body

(a)

According to the wiring diagram, which switch(s) should be

closed to switch on the headlights? Which light(s) will be switched on too? (5 marks) (b)

A two-way switch can be used so that the left and right

sidelights can be operated independently. Redraw a part of the circuit to show how this can be achieved. (1 mark)

3. In Christmas, serises of lights are used to decorate a christmas tree. A student thinks that if he connect one more serises to previous one serisely, the total brightness of the lights can be increased. (a) Does the student correct? Give reasons to support your answer. (5 marks) (b)

How can the student connect the two sets of lights so that the total

brightness of the lights can be increased? (1 mark) 4. A alarm clock is labeled as “3V”, and it needs two 1.5-V 'AA' cells to operate. (a) Which way should the cells be connected, serise or parallel? (1 mark) (b)

What is the physical meaning of 1.5-V labeled on a cell? (2 marks) (c)

What would happen if the polarity of one of the cells is reversed? (2 marks)

5. A torch requires three 1.5-V cells to work. When the switch is pushed up, the light bulb is on. (a)

Draw a simple labelled circuit diagram for the torch. (2 marks)

(b)

How will you modify the design of the torch so that it can be

switched on for a longer time? (1 mark) (c) Which device can be added in the circuit to control the brightness of the bulb? (1 mark)

6. The following figure shows a circuit diagram of a bulb using four 1.5-V cells to operate.

(a) Calculate the current passing the bulb when the switch closed.

(3 marks)

(b) Do charges are being used up, if not, then what is being used up in the circuit? (1 mark)

7. The figure below shows a 10 Ω bulb is connected to a variable resistor in parallel.

(a) How does the brightness of the bulb change if the contact is moved towards A? [1] (b) If the labelled working voltage of the bulb is 1.5 V, where should be the position of the contact placed? Show your calculation. (4 marks)

8. The following graph shows how the resistance changes with temperature of three different materials.

(a) When a tungsten light bulb is switched on, how does the current change with the first few minutes? Explain your answer. (3 marks) (b)

Suggest an application for thermister and explain your answer. (4 marks)

9. If a 7V rechargeable battery is labelled '1100 mAh', that means the battery can provide 1100 mA over one hour. If the camera operates for an hour at 1100 mA, how much charge has passed the battery? (2 marks)

10. The following figure shows a variable resistor. The resistance of the resistor can be changed when the contact moved.

*(a)

Explain briefly, with a simple diagram, how to change the

resistance of the resistor by moving the contact. (5 marks) (b) Suggest an application of variable resistor. (1 mark) 11. A student finds that both of the following circuits can change the brightness of the bulb.

(a) Explain why circuit A and circuit B can change the brightness of the bulb briefly? (4 marks) (b) Which circuit may switch off the bulb? Why not the other circuit, explain briefly? (3 marks)

12. A lighting system has three bulbs, (a) Which way should the bulbs be connected, series or parallel. Suggest a method to test the connection of the bulbs.

(3 marks)

(b) Draw a circuit diagram to show how the bulbs and the switch are connected. (3 marks) 13. The following figure shows a simple circuit.

(a) Draw a circuit diagram to show how the for the above circuit.

(3 marks)

(b) What happens to the brightness the bulbs when the switch is closed if internal resistance of the cells are negligible? Explain you answer briefly. (3 marks) (c) What happens to the brightness the bulbs when the switch is closed if internal resistance of the cells are NOT negligible? Explain you answer briefly. (3 marks)

14. A bulb is labeled as '3 V, 0.5 A' is connected in the circuit below. 12 V

A

B '3V, 0.5 A'

(a) A resistor should be connected across AB for the bulb to operate at its labeled value. What is the resistance of that resistor?

(3 marks)

(b) If only 15-Ω resistors are available, draw circuit to operate the bulb with 12V supply.

(2 marks)

15. A student connects the following circuit to find the resistance of the resistor with few ohms.

(a) In the circuit, what are the readings of the voltmeter and ammeter? (2 marks) (b) Draw a correct circuit for the student to find the resistance of a resistor with few ohms? (2 marks)

16. The following figure shows the V-I graphs of two resistors X and Y.

(a) Which resistor has a higher resistance? Explain your answer.

(2 marks)

(b) If X and Y are connected in series, in which region of the V-I graph, will the total resistance of the circuit lie?

(2 marks)

(c) If X and Y are connected in parallel, in which region of the V-I graph, will the total resistance of the circuit lie? (2 marks)

17. A student uses the following circuit to check the validity of the Ohm’s law (i.e. V = IR).

(a) If the resistance of the variable resistor is initially set to few ohms and then the resistance of it is increased slightly, what do the ammeter’s and voltmeter’s readings change?

(2 marks)

(b) If the resistance of the variable resistor is increased to 20 ki, why the reading of the ammeter and voltmeter do not follow the ohm’s law?

(3 marks)

Long questions 1. (a) A student measures the voltage across a cell. With the following two circuits.

In the circuit at the left, the voltmeter reading is 3 V. In the circuit at the left, the voltmeter reading is 2.5 V. (I) Compare the currents in the above circuits. Explain your answer briefly. (4 marks) (ii) Why is the reading of the voltmeter is different in the above circuit? (2 marks) (b) The following circuit can be used to measure the internal resistance of two identical cells.

The student the date of resistance and current in the following table. The results are as follows: R/W I/A

25 0.1

10 0.2

5 0.3

2.5 0.4

1 0.5

(I) Write down the relation between the total voltage of the cells, internal resistance of a cell r, current I and the resistance of variable resistor R. (1 mark) (ii) Using the data above find the internal resistance of cells. (4marks )

2. In a car, battery is connected to several applicants, lighting system, ventilation system, warming system etc. A driver switches on the two headlights and de-mister for few minutes before start the engine.

(a) If the headlights each draws 4 A and the de-mister draws 2 A. The p.d. across the battery drops from 14.6 V to 13.6 V when the headlights and de-misters are switched on. Then find the internal resistance of the battery? (2 marks) (b) When the driver switches on the starter, 90 A pass through the starter. Then what is the p.d. across the battery (internal resistance is NOT negligible)? (3 marks) (c) What is the voltage across the headlight while the starter motor and the demister are in use? What happens to the brightness of the headlight when current is passing through the starter? Explain briefly. (3 marks) (d) A car battery has to be replaced if its internal resistance increases to a certain value. How does a high internal resistance affect the work of a battery. (2 marks)

3. The following shows a set up of a circuit.

(a) Draw a circuit diagram the above setup with correct polarity of all apparatus. (5 marks) (b) How would the readings of the ammeter and the voltmeter change if the contact of the rheostat moves to right? Explain your answer briefly. (3 marks) (c) The following table shows the reading of V and A: (V) / V (A) / A

0.9 0.2

1.6 0.4

2.4 0.6

3.2 0.8

3.9 1.0

(I) Describe the process of the above experiment to obtain the data above? (3 mark) (ii) Plot a graph of V against I on graph paper. (4 marks) (iii) If the length of the eureka wire is doubled. On the graph in (ii), sketch the V-I relation. (1 mark)

4. The following circuit is used to study the p.d. across the bulb and also the current is pass through the bulb.

(b) Draw a circuit diagram for the above setup with correct polarity of all apparatus. (5 marks) (c)The following table shows the reading of the ammeter and voltmeter p.d.across the bulb (V) / V Current through the bulb (I) / A

1.0 0.3

1.8 0.6

2.8 0.9

4.0 1.3

5.0 1.6

6.4 1.9

(I) Plot a graph of V - I graph on graph paper. (4 marks) (ii) Why the graph does not show linear relation of V-I.

(2 marks)

(iii) What is the resistance of the light bulb when the p.d. across it is 2 V. (3 marks)

5. (a) Draw a circuit diagram to show how to measure the resistance of a high power light bulb (around 10 ohms only) by using the following component.

Component provided: a battery box, an ammeter, a voltmeter, a switch, a rheostat, a light bulb, several connecting wires (5 marks) (b) The following figure shows the voltmeter and the ammeter used in the experiment.

ammeter (0 − 500 mA)

voltmeter (0 − 5 V)

(I) What are the readings of the ammeter and the voltmeter means? (2 marks) (ii) What is the working power of the light, and how much energy is consumed in 10 minutes?

(3 marks)

(iii) What is the resistance of the light bulb? (2 marks) (c) If the p.d. across it increases, how do the temperature and the resistance of the light bulb change?

(2 marks)

6. The following sets up is used to measure the resistance of a light bulb.

Figure a (a) The above circuit is suitable for measure a resistance with few ohms only, explain it briefly. And draw a circuit diagram which is suitable for measure a resistance with several thousands ohms. (5 marks) (b) Figure b shows the voltmeter and the ammeter used in the experiment.

voltmeter (0 − 5 V)

ammeter (0 − 50 mA)

Figure b (I) What are the readings of the ammeter and the voltmeter means? (2 marks) (ii) What is the resistance of the light bulb?

(2 marks)

(c) Sketch a V-I graph for the above experiment, it is known that the temperature of the filament of the bulb increase with the p.d. across it. (4 marks)

(d) The variable resistor in the following circuit is use to control the pass the light

bulb.

(I) When the resistance of the variable resistor varies the change in the current is very small. Why?

(3 marks)

(ii) Modify a circuit so that a large change in the current when the variable resistor varies.

(2 marks)

7. The following circuit is used to find out the resistance of a eureka wire is affected by its

length.

Figure a (a) Find out the mistake in the above circuit.

(1 mark)

(b) Draw a correct circuit diagram the above setup with correct polarity of all apparatus.

(5 marks)

(c) The following results is obtained from a corrected circuit: Length of the wire l / m Voltage V / V Current I / A

0.1 0.5 0.5

0.2 1.0 0.5

0.3 1.4 0.5

0.4 1.9 0.5

(I) Plot a graph to show the relation between the length and the resistance of the eureka wire.

(4 marks)

(ii) Write down the relationship between the resistance and the length? (2 marks) (iii) If the thickness of the metal wire increases, how would the resistance of the wire be affected?

(2 marks)

-- End of Paper --