Electrostatics and Capacitors Generix Content - Electrostatics and Capacitors
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JAMB questions for "Physics :: Electrostatics and Capacitors"
Q1
Three cells each of e.m.f. 1.5V and internal resistance 2.5&#937; are connected as shown in the diagram. Find the net e.m.f. and the internal resistance.
A
4.5V, 0.83&#937;
B
4.5V, 7.50&#937;
C
1.5V, 0.83&#937;
D
1.5V, 7.50&#937;
E
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
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
200&#937;
B
300&#937;
C
500&#937;
D
100&#937;
E
Q4

The instataneous value of the induced e.m.f as a function of time is ε = ε0 sin ωt where ε0 is the peak value of e.m.f. The instantaneous value of the e.m.f., one quarter of the period, is

A

ε⁄ 4

B

ε0

C

0

D

ε⁄ 2

E
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 102 Ωm

B

2.55 x 105 Ωm

C

3.93 x 10-8 Ωm

D

3.93 x 10-6 Ωm

E
Q6
From the diagram above, the inductive reactance and the resistance R are respectively
A
25&#937; and 51&#937;
B
20&#937; and 50&#937;
C
10&#937; and 50&#937;
D
50&#937; and 45&#937;
E
Q7
The capacitance of a parallel-plate capacitor when in air is 3 &#956;F and in the presence of a dielectric material 6 &#956;F. The dielectric constant is
A
9
B
18
C
3
D
2
E
Q8
If the capacity of a capacitor is C= &#949;A/d, which of the following parameters is varied when a variable capacitor is used for tuning radio sets?
A
Constant (&#949;) and area
B
Distance only
C
Area and distance
D
Constant (&#949;) only
E
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
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
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
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
Q13

The resistance of a piece of wire of length 20m and cross-sectional area 8 x 10-6m2 is

A

8.0 x 10-12NC-1

B

8.0 x 109NC-1

C

4.0 x 109NC-1

D

4.0 x 10-11NC-1

E
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
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
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
Q17
An a.c circuit of emf 12V has a resistor of resistance 8&#937; connected in series to an inductor of inductive reactance 16&#937; and a capacitor of capacitive reactance 10&#937;. The current flow in the circuit is
A
1.4 A
B
1.2 A
C
12.0A
D
14.0A
E
Q18

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

A

XL = XC

B

XL  = 1/2 Xc

C

XL = 1/2XC

D

X= 2XC

E
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
Q20
Given three capacitors 0.3&#956;F, 0.5&#956;F and 0.2&#956;F, the joint capacitance when arranged to give minimum capacitance is
A
0.1&#956;F
B
0.3&#956;F
C
1.0&#956;F
D
0.5&#956;F
E
Q21
A cell whose internal resistance is 0.5&#937; 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
Q22

In the diagram beside, what would happen to the current, I, if another resistor, R2, is connected in parallel to R1

A

it will decrease if R2 is greater than R1

B

It will increase because the equivalent resistance will increase

C

It will decrease if R2 is less than R1

D

It will increase because the effective resistance will decrease

E
Q23
A wire of 5&#937; 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
20&#937;
B
5&#937;
C
40 &#937;
D
10&#937;
E
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
Q25
From the diagram below, determine the value of the resistance X.
A
9&#937;
B
12&#937;
C
15&#937;
D
6&#937;
E
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 104 J

D

4 x 102  J

E
Q27
An electric iron is rated 1000 W, 230 V. What is the resistance of its element?
A
57.6 &#937;
B
55.9  &#937;
C
52.9 &#937;
D
51.9 &#937;
E
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
Q29
The carbon-granule microphone works on the  principle of change in
A
voltage
B
inductance
C
resistance
D
capacitance
E
Q30
At what frequency would a capacitor of 2.5&#956;F used in a radio circuit have a reactance of 250 &#937;?
A
800Hz  &#960;
B
200&#960;  Hz
C
2000 &#960;  Hz
D
&#960;/800    Hz
E
Q31
A cell of internal resistance r supplies current to a 6.0&#937; resistor and its efficiency is 75%. Find the value of r.
A
8.0&#937;
B
4.5&#937;
C
2.0&#937;
D
1.0&#937;
E
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
Q33
At resonance, the phase angle in an a.c. circuit is
A
180°
B
90°
C
60°
D
E
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&#8730;2 A
B
2A
C
&#8730;2A
D
1A/ &#8730;2
E
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
Q36

The diagram beside shows three capacitors, C1, C2, and Cof capacitances 2µF, 6µF and 3µF respectively. The potential differences across C1, C2, and C3 respectively are

A

6V, 4V and 2V

B

6V, 2V and 4V

C

4V, 6V and 2V

D

2V, 6V and 4V

E
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
Q38
A cell of internal resistance 0.01&#937; can be measured accurately using the
A
Ohm- meter
B
potentiometer
C
electroscope
D
metre bridge
E
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
Q40
Four cells each of e.m.f. 1.5 V and internal resistance of 4&#937; are connected in parallel. What is the effective e.m.f and internal resistance of the combination ?
A
6.0 V, 16 &#937;
B
6.0V, 1&#937;
C
1.5 V , 4 &#937;
D
1.5V, 1&#937;
E
Q41
At what frequency would a 10 H inductor have a reactance of 2000&#937; ?
A
&#960;/200 Hz
B
&#960;/100 Hz
C
100/&#960; Hz
D
100&#960;Hz
E
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
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 104 J

B

3.0 X 10J

C

2.5 X 10-2 J

D

6.0 X 10-3 J

E
Q44
In the circuit below, the ammeter reads a current of 5.0A when R=8&#937; and reads 7.0A when R=5&#937;. The value of the unknown resistance X is
A
10.0&#937;
B
7.5&#937;
C
5.0&#937;
D
2.5&#937;
E
Q45

In the diagram below, if the internal resistance of the cell is zero, the ratio of the powers P1 and P2 dissipated by Rand R2 respectively, is

A

R2/R1

B

R/ R2

C

R1 + R2 /R1

D

R+ R2 /R2

E
Q46
The total resistance measured at PQ in the diagram above is
A
18.0 &#937;
B
11.0 &#937;
C
4.0 &#937;
D
2.0 &#937;
E
Q47

A parallel plate capacitor has a common plate area of 5 x 10-8 m2 and plate separation of 2 x 10-3 m . Assuming free space, what is the capacitance? ( Eo = 9.0 X 10-12 C2 N-1 M-2 )

A

2.25 x 10-1 F

B

4.50 x 10-17 F

C

2.25 X 1016 F

D

4.50 x 10-16 F

E
Q48
Which of the figures below shows the correct distribution of charges on an isolated positively charged hollow metal?
A
B
C
D
E
Q49
Three electric cells each of e.m.f. 1.5 V and internal resistance 1.0&#937; are connected in parallel across an external resistance of 2/3 &#937;. Calculate the value of the current in the resistor.
A
0.5 A
B
0.9 A
C
1.5A
D
4.5A
E
Q50
A galvanometer of internal resistance 50&#937; 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 &#937;
B
1950 &#937;
C
2000 &#937;
D
2 500 &#937;
E
Q51
In a meter bridge experiment, two resistors 2 &#937; and 3 &#937; 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
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
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
Q54
An alternating source is connected in series to a capacitor of capacity reactance of 103&#8730;3 and a resistor of resistance 103&#937;. The impedance of the circuit is
A
2 000 &#8730;3 &#937;
B
2000  &#937;
C
1000 &#8730;3 &#937;
D
1000 &#937;
E
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
Q56
In the circuit diagram below, calculate the current in the 12 -&#937; resistor if the cell has an e.m.f of 12V and an internal resistance of 1&#937;
A
0.8A
B
1.0A
C
1.6A
D
2.4A
E
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
Q58

Two resistors R1 = 4Ω and R2 =5Ω, are connected in parallel across a potential difference. If P1 and Prepresent the power dissipated in R1 and R2 respectively, then the ratio P1 : P2 is

A

4 : 5

B

5 : 4

C

16 : 25

D

25 : 16

E
Q59

A parallel plate capacitor of area 10cm2 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 10m

E
Q60
A 40 W instrument has a resistance of 90&#937;. On what voltage should it be operated normally?
A
60 V
B
150 V
C
225 V
D
3600 V
E