##### TMA

# TMA2/PHY102 – Electricity, Magnetism and Modern Physics

## TMA Quiz Questions

TMA: TMA2/PHY102

PHY102 – Electricity, Magnetism and Modern Physics

Mr. Ibanga Efiong (eibanga@noun.edu.ng )

1 Calculate the potential difference between the plates of a parallel plate capacitor so that the gravitational force on a proton would be balanced by the electric field (proton mass =

1.67×10−27kg

1.67×10−27kg

, electronic charge

e=1.6×10−19C

e=1.6×10−19C

, plate separation is 0.5cm. Take

g=9.8m/s2)

g=9.8m/s2)

A. 1.4×10−6V

1.4×10−6V

B. 2.0×10−6V

2.0×10−6V

C. 1.7×10−6V

1.7×10−6V

D. 3.2×10−6V

3.2×10−6V

2 Select the correct option from the following

A. electric field is a scalar quantity

B. electromotive force is a vector quantity

C. electric current is a scalar quantity

D. eletric potential is a vector quantity

3 the electrical force on a negative charge located near an isolated positive charge

A. points away from the isolated charge

B. is tangent to a circle centred about the isolated charge

C. points toward the isolated charge

D. is zero

4 The average velocity of the electrons in a piece of wire of cross-sectional area

2.0×10−6m2

2.0×10−6m2

is

2.5×10−4m/s

2.5×10−4m/s

when a steady current of 4.0 A is flowing. Calculate the number of free electrons per unit volume of the material

A. 3×1019

3×1019

B. 5×1020

5×1020

C. 2×1023

2×1023

D. 5×1028

5×1028

5 A 0.40 mm diameter copper wire carries a current of

3μA

3μA

. Find the current density in the wire

A. 15.16A/m2

15.16A/m2

B. 33.32A/m2

33.32A/m2

C. 26.17A/m2

26.17A/m2

D. 23.87A/m2

23.87A/m2

6 Calculate the resistance of 180 m of silver wire having a cross section of

0.33mm2

0.33mm2

. The resistivity of silver is

1.6×10−8Ωm

1.6×10−8Ωm

A. 11.2Ω

11.2Ω

B. 9.6Ω

9.6Ω

C. 14.6Ω

14.6Ω

D. 7.5Ω

7.5Ω

7 A wire with resistance of

8.0Ω

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.

A. 72Ω

72Ω

B. 60Ω

60Ω

C. 80Ω

80Ω

D. 45Ω

45Ω

8 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?

A. v/4

B. v/2

C. 2v

D. 4v

9 A coil of wire has a resistance of

25.0Ω

25.0Ω

at

20oC

20oC

and a resistance of

25.1Ω

25.1Ω

at 35

oC

oC

What is its temperature coefficient of of resistance?

A. 4.5×10−4/oC

4.5×10−4/oC

B. 3.5×10−3/oC

3.5×10−3/oC

C. 2.6×10−4/oC

2.6×10−4/oC

D. 4.0×10−5/oC

4.0×10−5/oC

10 A copper wire has resistance of

2.0Ω

2.0Ω

at

0oC

0oC

and

2.26Ω

2.26Ω

at

30oC

30oC

. What is its resistance at

50oC

50oC

?

A. 2.43Ω

2.43Ω

B. 3.34Ω

3.34Ω

C. 1.52Ω

1.52Ω

D 5.31Ω

5.31Ω

11 The current I in a conductor as a function of time t is given as

I(t)=5t2−3t+10

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?

A. 154.4C

B. 193.5C

C. 225.5C

D. 300.0C

12 A nicrome wire is 1.0m long and

1.0mm2

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.

A. (2MΩm)−1

(2MΩm)−1

B. (4kΩm)−1

(4kΩm)−1

C. (2mΩm)−1

(2mΩm)−1

D. (4Ωm)−1

(4Ωm)−1

13 A battery charger supplies 10 A to charge a storage battery which has an open – circuit voltage of 5.6 V. If the voltmeter connected across the charger reads 6.8V, what is the internal resistance of the battery at this time?

A. 1.3Ω

1.3Ω

B. 0.52Ω

0.52Ω

C. 0.12Ω

0.12Ω

D. 2.1Ω

2.1Ω

14 A battery of e.m.f. and negligible internal resistance is connected to two resistors of resistances

R1

R1

and

R−2

R−2

as shown in the figure. What is the potential difference across the resistor of resistance

R2

R2

A. E(R1+R2)/R1

E(R1+R2)/R1

B. ER2/(R1+R2)

ER2/(R1+R2)

C. E(R1+R2)/R2

E(R1+R2)/R2

D. ER2R1

ER2R1

15 A battery has emf 13.2V and internal resistance

24mΩ

24mΩ

. If the load current is 20.0A, find the terminal voltage o f the battery

A. 12.7V

B. 14.5V

C. 16.8V

D. 17.7V

16 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?

A. N1.50

B. N25.30

C. N32.40

D. N52.20

17 A

2Ω

2Ω

and a

3Ω

3Ω

resistors in parallel are connected in series to a

4Ω

4Ω

resistor.The combination is then connected across a 12V battery having internal resistance of

1Ω

1Ω

as shown in the figure. What is the equivalent resistance of the circuit?

Click here to see exhibit

A. 9.2Ω

9.2Ω

B. 6.2Ω

6.2Ω

C. 2.2Ω

2.2Ω

D. 7.2Ω

7.2Ω

18 Calculate the currents in the circuit

Click here to see exhibit

A. 1.94A

B. 1.36A

C. 3.23A

D. 5.45A

19 Calculate the currents in

3Ω

3Ω

resistor

Click here to see exhibit

A. 0.36A

B. 2.54A

C. 1.42A

D. 3.46A

20 The term ‘lost volts’ refers to ———–

A. energy per coulomb dissipated in the external (load) resistance

B. terminal potential difference

C. energy per coulomb dissipated in the internal resistance of the source of emf

D. energy per coulomb wasted to heat up the connecting wires