##### TMA

# TMA4/PHY102 – Electricity, Magnetism and Modern Physics

## TMA Quiz Questions

TMA: TMA4/PHY102

PHY102 – Electricity, Magnetism and Modern Physics

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

1 An emf of 5V is suddenly applied to an LR circuit. The value of the resistor in the circuit is 15 . At one inductive time constant, what is the rate at which energy is delivered by the battery?

A. 1.05W

B. 5.78W

C. 120.42W

D. 12.24W

2 A certain inductor has an indutance of 0.50H and a resistance of 2.0. It is placed in series with a swtich, a 12.0-V battery and a 4.0 ohms resistor. Find the time constant of the circuit and the energy stored in the inductor.

A. 0.83s and 100J

B. 0.032s and 20J

C. 0.47s and 5J

D. 0.083s and 1J

3 A rod of 5.0m length is held horizontally and with its axis in an east-west direction. It is allowed to fall straight down. What is the emf induced in it when its speed is 3.0m/s if the earth’s magnetic field is 06010−4T with a dip angle of 53 degrees?

A. 5410−4V

B. 3610−3

C. 2010−5

D. 4210−4

4 A rectangular wire loop of width 4.0cm is being pulled out of a magnetic field at a constant speed of 2.0m/s. The magnetic field is 0.30T and is uniform in the region, perpendicular and into the plane of the loop. What is the induced emf in the loop?

A. 0.056V

B. 0.012V

C. 0.024V

D. 0.087V

5 A 0.96H coil carries a current of 8.0A. Calculate the energy stored in it

A. 30.7J

B. 45.3J

C. 62.6J

D. 27.3J

6 A 1000-turn solenoid of length 20cm has a cross-sectional area of 2.0 square centimetre. Find the inductance of the coil if the core is air.

A. 12610−3H

B. 23010−3H

C. 46610−3H

D. $1.54\times10^{-3}H

7 A coil of inductance 2.0H and resistance 5 is connected to a 30V battery. Calculate the rate of current growth in the coil when the circuit has just been made and when the current reaches one-half of its steady-state vaule.

A. 15A/s and 7.5A/s

B. 3.5A/s and 10A/s

C. 12A/s and 4.4A/s

D. 6.2A/s and 18A/s

8 A 1000-turns coil of cross-sectional area 30cm2 rotates at a frequency of 120 Hz in a magnetic field 0.1 T. Calculate the peak value of the induced emf

A. 346.4V

B. 112.3V

C. 97.6V

D. 226.2V

9 A certain generator consists of a rectangular coil of 250 turns and an area of 50cm2. The coil rotates at a speed of 100 revolutions per second in a horizontal magnetic field 0.3T. Calculate the maximum induced emf in the coil and the induced emf when the plane of the coil is inclined at an angle of 35o to the horizontal

A. 235.6V and 193.0V

B. 344.2V and 230.2V

C. 144.3V and 96.5V

D. 56.4V and 26.7V

10 At which of the following values of t is the magnitude of the emf induced in the coil a maximum if a magnetic field perpendicular to the plane of a flat coil of copper wire has a time variation of the magnetic flux density given by B=Bosin(2tT) where Bois the peak value of the magnetic flux density and T the period

A. T/8

B. T/4

C. 3T/8

D. T/2

11 An air-cored transformer is assumed to be 100% efficient. The ratio of the secondary turns to the primary turns is 1:20. A 240V ac supply is connected to the primary coil and a 6 load is connected to the secondary coil. what is the current in the primary coil?

A. 0.10A

B. 0.14A

C. 2.0A

D. 40.0A

12 A voltmeter connected across a 60Hz ac source reads 240V. Write down the expression of the instanteneous voltage as a function of time.

A. 240sin339.4t

B. 339.4sin377t

C. 377cos339.4t

D. 240cos339.4t

13 An ac circuit consists of a voltage source v=200sin120t and a 6F capacitor in series. Calculate the current established in the circuit

A. 0.32A

B. 1.24A

C. 0.64A

D. 2.13A

14 An RLC circiut contains an ac voltage source with rms value of 50V and has a frequency of 600Hz. Suppose that a resistance R = 20 , capacitance C = 10.0 F and an inductance L = 4.0mH are connected in series to the source. Find the current in the circuit and the voltmeter reading across the inductor.

A. 2.17A and 32.8V

B. 1.6A and 24.2V

C. 0.13A and 12.1V

D. 4.0A and 23.1V

15 An RLC circuit is used to tune a radio set to receive NOUN RADIO broadcasting at 105.9MHz in the FM band. The resistance and the inductance of the circuit of the radio set are 12 and 1.4H respectively. What capacitance should the circuit have?

A. 1.64pF

B. 1.51F

C. 1.33mF

D. 2.11pF

16 The work function of a metal is 3.45eV. Calculate th maximum wavelength of a photon that can eject photelectrons from the metal

A. 1610−6m

B. 3610−7m

C. 2410−8m

D. 3410−7m

17 When a copper surface is illuminated by radiation of wavelength 2537 angstrome units the value of the stopping potential is found to be 0.24volts. Calculate the work function of copper.

A. 4.48eV

B. 7.46eV

C. 3.26eV

D. 2.67eV

18 A spectral line is emitted when an atom undergoes transition between two levels with a difference in energy of 2.4eV. What is the wavelength of the line?

A. 287nm

B. 507angstrome units

C. 377angstrome units

D. 518nm

19 The half-life of a certain radioactive isotope is 32 hours. What fraction of the sample would remain after 16 huors?

A. 0.50

B. 0.25

C. 0.62

D. 0.71

20 A potentiometer wire of length 100cm has a resistance of 10. It is connected in series to to a resistance R and a cell of emf 2V and negligible internal resistance. A source of emf of 10mV is balanced by a length of 40cm of the potentiometer wire. What is the value of the resistance R?

A. 200

B. 950

C. 2000

D. 790

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Pls I really need the following course tmas;mth212 mth282 mth232 phy202 phy204 phy206 and phy208