"Electrostatics and Capacitors" question number distribution across years

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Physics index on skoool nigeria

JAMB questions for "Physics :: Electrostatics and Capacitors"

Q1

Three cells each of e.m.f. 1.5V and internal resistance 2.5Ω are connected as shown in the diagram. Find the net e.m.f. and the internal resistance.

A

4.5V, 0.83Ω

B

4.5V, 7.50Ω

C

1.5V, 0.83Ω

D

1.5V, 7.50Ω

E

**Answer:** C

Q2

If two charged plates are maintained at a potential different of 3k V, the work in taking a charge of 600 µC across the field is

A

1.8J

B

18.0J

C

0.8J

D

9.0J

E

**Answer:** D

Q3

A 120 V, 60W lamp is to be operated on 220 V a.c. supply mains. Calculate the value of non-inductive resistance that would be required to ensure that the lamp is run on correct value

A

200Ω

B

300Ω

C

500Ω

D

100Ω

E

**Answer:** A

Q4

The instataneous value of the induced e.m.f as a function of time is ε = ε_{0} sin ωt where ε_{0} is the peak value of e.m.f. The instantaneous value of the e.m.f., one quarter of the period, is

A

ε_{0 }⁄ 4

B

ε_{0}

C

0

D

ε_{0 }⁄ 2

E

**Answer:** B

Q5

A conductor has a diameter of 1.00mm and length 2.00m. If the resistance of the material is 0.1Ω,its resistivity is

A

2.55 x 10^{2} Ωm

B

2.55 x 10^{5} Ωm

C

3.93 x 10^{-8} Ωm

D

3.93 x 10^{-6} Ωm

E

**Answer:** C

Q6

From the diagram above, the inductive reactance and the resistance R are respectively

A

25Ω and 51Ω

B

20Ω and 50Ω

C

10Ω and 50Ω

D

50Ω and 45Ω

E

**Answer:** C

Q7

The capacitance of a parallel-plate capacitor when in air is 3 μF and in the presence of a dielectric material 6 μF. The dielectric constant is

A

9

B

18

C

3

D

2

E

**Answer:** D

Q8

If the capacity of a capacitor is C= εA/d, which of the following parameters is varied when a variable capacitor is used for tuning radio sets?

A

Constant (ε) and area

B

Distance only

C

Area and distance

D

Constant (ε) only

E

**Answer:** C

Q9

The production and type of charge of a body can only be accounted for by the

A

deficiency or surplus of neutrons

B

equilibrium in protons and neutrons

C

deficiency or surplus of protons

D

deficiency or surplus of electrons

E

**Answer:** D

Q10

A cell of internal resistance r is connected to an external resistor R. The condition for maximum power transfer is

A

R > r

B

R

C

R = 2r

D

R = r

E

**Answer:** D

Q11

In an a.c circuit that contains only a capacitor, the voltage lags behind the current by

A

90°

B

180°

C

60°

D

30°

E

**Answer:** B

Q12

If two inductors of inductances 3H and 6H are arranged in series, the total inductances is

A

18.0 H

B

9.0 H

C

2.0 H

D

0.5 H

E

**Answer:** B

Q13

The resistance of a piece of wire of length 20m and cross-sectional area 8 x 10^{-6}m^{2} is

A

8.0 x 10^{-12}NC^{-1}

B

8.0 x 10^{9}NC^{-1}

C

4.0 x 10^{9}NC^{-1}

D

4.0 x 10^{-11}NC^{-1}

E

**Answer:** A

Q14

If the distance between two point charges is increased by a factor of four, the magnitude of the electrostatic force between them will be

A

1/2 of its former value

B

1/4 of its former value

C

1/16 of its former value

D

4 times its former value

E

**Answer:** C

Q15

In the circuit of a transistor beside, the terminals P,Q, and R represent

A

COLLECTOR, EMITTER, and BASE

B

EMITTER, BASE and COLLECTOR

C

BASE, EMITTER, and COLLECTOR

D

BASE, COLLECTOR, and EMITTER

E

**Answer:** B

Q16

The figure below shows three capacitors 2µF, 3µF and 6µF connected in series. If the p.d across the system is 12V, the p.d across the 6µF capacitor is

A

4V

B

6V

C

12V

D

2V

E

**Answer:** D

Q17

An a.c circuit of emf 12V has a resistor of resistance 8Ω connected in series to an inductor of inductive reactance 16Ω and a capacitor of capacitive reactance 10Ω. The current flow in the circuit is

A

1.4 A

B

1.2 A

C

12.0A

D

14.0A

E

**Answer:** B

Q18

In a tuned radio receiver R, L, C series circuit for resonance, the inductive and capacitive reactance X_{L} and X_{C} respectively are related as

A

X_{L} = X_{C}

B

X_{L } = 1/2 X_{c}

C

XL = 1/2X_{C}

D

X_{L }= 2X_{C}

E

**Answer:** A

Q19

The instrument used for securing a large number of similar charges by induction is called

A

electrophorus

B

capacitor

C

proof-plane

D

electroscope

E

**Answer:** A

Q20

Given three capacitors 0.3μF, 0.5μF and 0.2μF, the joint capacitance when arranged to give minimum capacitance is

A

0.1μF

B

0.3μF

C

1.0μF

D

0.5μF

E

**Answer:** A

Q21

A cell whose internal resistance is 0.5Ω delivers a current of 4 A to an external resistor. The lost voltage of the cell is

A

1.250V

B

2.000V

C

8.000V

D

0.125V

E

**Answer:** B

Q22

In the diagram beside, what would happen to the current, I, if another resistor, R_{2}, is connected in parallel to R_{1}

A

it will decrease if R_{2} is greater than R_{1}

B

It will increase because the equivalent resistance will increase

C

It will decrease if R_{2} is less than R_{1}

D

It will increase because the effective resistance will decrease

E

**Answer:** D

Q23

A wire of 5Ω resistance is drawn out so that its new length is two times the original length. If the resistivity of the wire remains the same and the cross-sectional area is halved, the new resistance is

A

20Ω

B

5Ω

C

40 Ω

D

10Ω

E

**Answer:** A

Q24

A positively charged rod X is brought near an uncharged metal sphere Y and is then touched by a finger with X still in place . When the finger is removed, the result is that Y has

A

a negative charge and a positive potential

B

no charge and a zero potential

C

a negative charge and a negative potential

D

a positive charge and a zero potential

E

**Answer:** A

Q25

From the diagram below, determine the value of the resistance X.

A

9Ω

B

12Ω

C

15Ω

D

6Ω

E

**Answer:** C

Q26

The energy stored in a capacitor of capacitance 10μC is

A

4 x 10^{-3} J

B

5 x 10^{-4 }J

C

5 x 10^{4} J

D

4 x 10^{2} J

E

**Answer:** B

Q27

An electric iron is rated 1000 W, 230 V. What is the resistance of its element?

A

57.6 Ω

B

55.9 Ω

C

52.9 Ω

D

51.9 Ω

E

**Answer:** C

Q28

A transistor is used in the amplification of signals because it

A

allows doping

B

contains electron and hole carriers

C

consumes a lot of power

D

controls the flow of current

E

**Answer:** B

Q29

The carbon-granule microphone works on the principle of change in

A

voltage

B

inductance

C

resistance

D

capacitance

E

**Answer:** C

Q30

At what frequency would a capacitor of 2.5μF used in a radio circuit have a reactance of 250 Ω?

A

800Hz
π

B

200π Hz

C

2000 π Hz

D

π/800 Hz

E

**Answer:** A

Q31

A cell of internal resistance r supplies current to a 6.0Ω resistor and its efficiency is 75%. Find the value of r.

A

8.0Ω

B

4.5Ω

C

2.0Ω

D

1.0Ω

E

**Answer:** C

Q32

A capacitor of 20 x 10-12F and an inductor are joined in series. The value of the inductance that will give the circuit a resonant frequency of 200 kHz is

A

1/8 H

B

1/16 H

C

1/32 H

D

1/64 H

E

**Answer:** C

Q33

At resonance, the phase angle in an a.c. circuit is

A

180°

B

90°

C

60°

D

0°

E

**Answer:** B

Q34

The current through a resistor in an a.c circuit is given as 2 sin wt. Determine the d.c equivalent of current

A

2√2 A

B

2A

C

√2A

D

1A/ √2

E

**Answer:** C

Q35

A transistor functions mainly as a

A

charge storer and a switch

B

switch and an amplifier

C

rectifier and an amplifier

D

charge storer and an amplifier

E

**Answer:** C

Q36

The diagram beside shows three capacitors, C_{1}, C_{2,} and C_{3 }of capacitances 2µF, 6µF and 3µF respectively. The potential differences across C_{1}, C_{2}, and C_{3} respectively are

A

6V, 4V and 2V

B

6V, 2V and 4V

C

4V, 6V and 2V

D

2V, 6V and 4V

E

**Answer:** B

Q37

The diagram below shows two capacitors P and Q of capacitance 2µF and 4µF respectively connected to a d.c source. The ratio energy stored in P to Q is

A

1:4

B

1:2

C

2:1

D

4:1

E

**Answer:** B

Q38

A cell of internal resistance 0.01Ω can be measured accurately using the

A

Ohm- meter

B

potentiometer

C

electroscope

D

metre bridge

E

**Answer:** B

Q39

The diagram below shows two capacitors P and Q of capacitances 5µF and 10µF. Find the charges stored in P and Q respectively.

A

200µC and 100µC

B

100µC and 200µC

C

4µC and 2µC

D

2µC and 4µC

E

**Answer:** B

Q40

Four cells each of e.m.f. 1.5 V and internal resistance of 4Ω are connected in parallel. What is the effective e.m.f and internal resistance of the combination ?

A

6.0 V, 16 Ω

B

6.0V, 1Ω

C

1.5 V , 4 Ω

D

1.5V, 1Ω

E

**Answer:** D

Q41

At what frequency would a 10 H inductor have a reactance of 2000Ω ?

A

π/200 Hz

B

π/100 Hz

C

100/π Hz

D

100πHz

E

**Answer:** C

Q42

In a series R-L-C circuit at resonance, the voltages across the resistor and inductor are 30 V and 40 V respectively. What is the voltage across the capacitor?

A

30 V

B

40 V

C

50 V

D

70 V

E

**Answer:** B

Q43

In the circuit below, the potential across each capacitor is 100V. The total energy stored in the two capacitors is

A

3.0 X 10^{4} J

B

3.0 X 10^{2 }J

C

2.5 X 10^{-2} J

D

6.0 X 10^{-3} J

E

**Answer:** C

Q44

In the circuit below, the ammeter reads a current of 5.0A when R=8Ω and reads 7.0A when R=5Ω. The value of the unknown resistance X is

A

10.0Ω

B

7.5Ω

C

5.0Ω

D

2.5Ω

E

**Answer:** D

Q45

In the diagram below, if the internal resistance of the cell is zero, the ratio of the powers P_{1} and P_{2} dissipated by R_{1 }and R_{2} respectively, is

A

R_{2}/R_{1}

B

R_{1 }/ R_{2}

C

R_{1} + R_{2} /R_{1}

D

R_{1 }+ R_{2} /R_{2}

E

**Answer:** A

Q46

The total resistance measured at PQ in the diagram above is

A

18.0 Ω

B

11.0 Ω

C

4.0 Ω

D

2.0 Ω

E

**Answer:** C

Q47

A parallel plate capacitor has a common plate area of 5 x 10^{-8} m^{2} and plate separation of 2 x 10^{-3} m . Assuming free space, what is the capacitance? ( Eo = 9.0 X 10^{-12} C^{2} N^{-1} M^{-2} )

A

2.25 x 10^{-1} F

B

4.50 x 10^{-17 }F

C

2.25 X 10^{16 }F

D

4.50 x 10^{-16} F

E

**Answer:** C

Q48

Which of the figures below shows the correct distribution of charges on an isolated positively charged hollow metal?

A

B

C

D

E

**Answer:** C

Q49

Three electric cells each of e.m.f. 1.5 V and internal resistance 1.0Ω are connected in parallel across an external resistance of 2/3 Ω. Calculate the value of the current in the resistor.

A

0.5 A

B

0.9 A

C

1.5A

D

4.5A

E

**Answer:** C

Q50

A galvanometer of internal resistance 50Ω has a full scale deflection for a current of 5 mA. What is the resistance required to convert it to a voltmeter with full scale deflection of 10 V?

A

1 750 Ω

B

1950 Ω

C

2000 Ω

D

2 500 Ω

E

**Answer:** B

Q51

In a meter bridge experiment, two resistors 2 Ω and 3 Ω occupy the left and right gaps respectively. Find the balance point from the left side of the bridge.

A

20 cm

B

40 cm

C

60 cm

D

80 cm

E

**Answer:** B

Q52

Two 50μF parallel plate capacitors are connected in series . The combined capacitor is then connected across a 100-V battery. The charge on each plate of the capacitor is

A

5.00 X 10^{-5} C

B

2.50 x 10^{-3 }C

C

1.25 x 10^{-3} C

D

1.00 x 10^{-2} C

E

**Answer:** B

Q53

The purpose of a dielectric material in a parallel plate capacitor is to

A

increase its capacitance

B

decrease its capacitance

C

insulate the plates from each other

D

increase the magnetic field between the plates

E

**Answer:** A

Q54

An alternating source is connected in series to a capacitor of capacity reactance of 103√3 and a resistor of resistance 103Ω. The impedance of the circuit is

A

2 000 √3 Ω

B

2000 Ω

C

1000 √3 Ω

D

1000 Ω

E

**Answer:** B

Q55

The resultant capacitance in the figure below is

A

15.0 µF

B

9.8 µF

C

1.3 µF

D

0.8 µF

E

**Answer:** D

Q56

In the circuit diagram below, calculate the current in the 12 -Ω resistor if the cell has an e.m.f of 12V and an internal resistance of 1Ω

A

0.8A

B

1.0A

C

1.6A

D

2.4A

E

**Answer:** A

Q57

A capacitor 8 µF, is charged to a potential difference of 100V. The energy stored by the capacitor is

A

1.0 x 104 J

B

8.0 x 10 J

C

1.25 X 10 J

D

4.0 X 10-2 J

E

**Answer:** D

Q58

Two resistors R_{1} = 4Ω and R_{2} =5Ω, are connected in parallel across a potential difference. If P_{1} and P_{2 }represent the power dissipated in R_{1} and R_{2} respectively, then the ratio P_{1} : P_{2} is

A

4 : 5

B

5 : 4

C

16 : 25

D

25 : 16

E

**Answer:** B

Q59

A parallel plate capacitor of area 10cm^{2} in vacuum has a capacitance of 10^{-2 }µF. What is the distance between the plates ? (εo=9 x 10^{-12} Fm ^{-1})

A

9 x 10^{-13} m

B

9 x 10^{-7} m

C

9 x 10^{-3} m

D

9 x 10^{7 }m

E

**Answer:** C

Q60

A 40 W instrument has a resistance of 90Ω. On what voltage should it be operated normally?

A

60 V

B

150 V

C

225 V

D

3600 V

E

**Answer:** A