Electricity and Magnetism Answers

10 A cirrent flows in a wire of circular cross-section with the free electrons travelling with a mean drift velocity v. If an equal current flows in a wire of the same material but of twice theradius, what is the new mean drift velocity?
v/4
v/2
2v
4v

11 A wire with resistance of
8.0Ω
is drawn out through a die so that its new length is three times its original length. Find the resistance of the longer wire assuming that the resistivity and density of the material are unaffected by the drawing process.
72Ω
60Ω
80Ω
45Ω

17 A copper wire has resistance of
2.0Ω
at
0oC
and
2.26Ω
at
30oC
. What is its resistance at
50oC
?
2.43Ω
3.34Ω
1.52Ω
5.31Ω

18 A coil of wire has a resistance of
25.0Ω
at
20oC
and a resistance of
25.1Ω
at 35
oC
What is its temperature coefficient of of resistance?
4.5×10−4/oC
$3.5×10−3/oC
2.6×10−4/oC
4.0×10−5/oC

19 A cirrent flows in a wire of circular cross-section with the free electrons travelling with a mean drift velocity v. If an equal current flows in a wire of the same material but of twice theradius, what is the new mean drift velocity?
v/4
v/2
2v
4v

20 A wire with resistance of
8.0Ω
is drawn out through a die so that its new length is three times its original length. Find the resistance of the longer wire assuming that the resistivity and density of the material are unaffected by the drawing process.
72Ω
60Ω
80Ω
45Ω

14 Electrical energy is sold by PHCN in units of kilowatt-hour (kWh). The lighting of a house is done with five 60W bulbs which are swithed on for approximately three hours per day. What is the lighting bill for the household over a period of 30days at the rate of N1.20 per kilowatt-hour?
N1.50
N25.30
N32.40
N52.20

15 A battery has emf 13.2V and internal resistance
24mΩ
. If the load current is 20.0A, find the terminal voltage o f the battery
12.7V
14.5V
16.8V
17.7V

Points A and B each have an electric potential of +12 V. How much work would be required to take 3 C of positive charge from A to B?
0 J
3 J
9 J
36 J

2 The electric potential difference between two points A and B is 42 V. What is the work done by an external agent in carrying a charge of
5.0×10−5C
from A to B at constant speed?
2.1×10−3J
8.4×10−4J
21×10−4J
8.4×10−3J

19 If the steady current in a wire is coming directly toward you, the magnetic field lines
point radially outward
radially inward
circle the wire in the clockwise direction
circle the wire in the counter clockwise direction

20 One end of a simple rectangular wire-loop current balance is inserted into a solenoid. A force of
3.0×10−3N
is found to act on this end when a current of 2.0 A is flowing in it. If the length of the conductor forming the end of the the wire-loop is 0.
0.043T
0.26T
0.43T
0.015T

What is the self - inductance of an air-core solenoid, 1m long and 0.05m in diameter, if it has 1400 turns?
5.23mH
4.84mH
3.63mH
2.42mH

17 Which of the following is NOT correct?
A changing electric field can produce a changing magnetic field
A steady magnetic field produces a steady current
A changing magnetic field can produce a changing current
A changing magnetic field can produce a steady electric field

18 A rectangular coil of dimensions 20cm by 15cm lies with its plane parallel to a magnetic field of
0.5W/m2
. The coil, carrying a current of 10A experiences a torque of 4.5Nm in the field. How many loops has the coil?
100
60
30
20

What is the self - inductance of an air-core solenoid, 1m long and 0.05m in diameter, if it has 1400 turns?
5.23mH
4.84mH
3.63mH
2.42mH

17 Which of the following is NOT correct?
A changing electric field can produce a changing magnetic field
A steady magnetic field produces a steady current
A changing magnetic field can produce a changing current
A changing magnetic field can produce a steady electric field

18 A rectangular coil of dimensions 20cm by 15cm lies with its plane parallel to a magnetic field of
0.5W/m2
. The coil, carrying a current of 10A experiences a torque of 4.5Nm in the field. How many loops has the coil?
100
60
30
20

6 Calculate the currents in $3\Omega$ resistor
0.36A
2.54A
1.42A
3.46A

7 Calculate the currents in the circuit
1.94A
1.36A
3.23A
5.45A

8 Electrical energy is sold by PHCN in units of kilowatt-hour (kWh). The lighting of a house is done with five 60W bulbs which are swithed on for approximately three hours per day. What is the lighting bill for the household over a period of 30days at the rate of N1.20 per kilowatt-hour?
N1.50
N25.30
N32.40
N52.20

9 A battery has emf 13.2V and internal resistance $24m\Omega$. If the load current is 20.0A, find the terminal voltage o f the battery
12.7V
14.5V
16.8V
17.7V

10 A cirrent flows in a wire of circular cross-section with the free electrons travelling with a mean drift velocity v. If an equal current flows in a wire of the same material but of twice theradius, what is the new mean drift velocity?
v/4
v/2
2v
4v

19 A nichrome wire is 1.0m long and
1.0mm2
in cross-sectional area. It carries a current of 4.0 A when a potential difference of 2 V is applied between its ends. Calculate the conductivity of the wire.
(2MΩm)−1
(4kΩm)−1
(2mΩm)−1
(4Ωm)−1

20 The current I in a conductor as a function of time t is given as
I(t)=5t2−3t+10
where current is in ampres A and t is in seconds s. What quantity of charge moves across a section through the conductor during the interval t=2s to t=5s?
154.4C
193.5C
225.5C
300.0C

A uniform electric field of 200 N/C is in the x-direction. A point charge of
3μC
is released from rest at the origin. What is the kinetic energy of the charge when it is at x = 4 m?
2.4×10−2J
1.6×10−2J
3.6×10−2J
4.8×10−2J