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1995 - JAMB Physics Past Questions and Answers - page 4

31

If a resistance is halved in value and the potential difference across it is tripled, then the ratio of the new current to the old one is

A
1 : 6
B
1 : 3
C
2 : 1
D
6 : 1
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32

A 12V battery has an internal resistance of 0.5W.If a cable of 1.0W resistance is connected across the two terminals of the battery, the current drawn from the battery is

A
16.0A
B
8.0A
C
0.8A
D
0.4A
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33

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

A
increase its capacitance
B
decrease its capacitance
C
insulate the plate from each other
D
increase the magnetic field between the plates
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34

An electric current of 2 amperes flows in a heating coil of resistance 50 ohms for 3 minutes 20 seconds. Determine the heat produced

A
0.5kJ
B
8.0kJ
C
20.0kJ
D
40.0kJ
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35

If the maximum voltage across a 100ohms resistor is 20V, then the maximum power it can dissipate is

A
5.00W
B
4.00W
C
2.00W
D
25W
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36

Which of the following is required to convert a milliammeter to an ammeter?

A
A high resistance in parallel
B
A high resistance in series
C
A low resistance in parallel
D
A low resistance in series
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37

The primary winding of a transformer has 400 turns and its secondary has 100 turns. If a source of e.m.f. of 12V is applied to the primary, the secondary e.m.f. will be

A
3V
B
6V
C
24V
D
48V
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38

A light of energy 5eV falls on a metal and the electrons with a maximum kinetic energy of 2eV are ejected. The work function of the metal is

A
0.4eV
B
2.5eV
C
3.0eV
D
7.0eV
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39

The half-life of a radio-active element is 9 days, what fraction of atoms has decayed in 36 days?

A
\( \frac{1}{16} \)
B
\( \frac{1}{4} \)
C
\( \frac{1}{2} \)
D
\( \frac{15}{16} \)
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40

An alternating source is connected in series to a capacitor of capacity reactance ( 10^3 \sqrt{3} ) and a resistor of resistance 103 Ohms. The Impedance of the circuit is...

A
\( 2000 \sqrt{3} \) Ohms
B
2000 Ohms
C
\( 1000 \sqrt{3} \) Ohms
D
1000 Ohms
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