2. In India, distribution of electricity for domestic purpose is done in the form of
220 V; 50 Hz
110 V; 60 Hz
220 V; 60 Hz
110 V; 50 Hz
3. When an electrical safety fuse is rated (marked) as 16 A, it means it
will not work if current is less than 16 A
has a resistance of 16 Ω
will work if the temperature is more than 16°C
will be blown (break) if current exceeds 16 A
4. The main power supply in India is at 220 V, whereas that in the US is at 110 V. Which one among the following statements in this regard is correct?
110 V is safer but more expensive to maintain
110 V is safer and cheaper to maintain
110 V leads to lower power loss
110 V works better at higher latitudes
Answer (a). The higher the voltage, the lesser the current. The lesser the current the lesser the loss of power in transmission. Thus with 110 v the loss of power makes it more expensive. On the other hand, higher voltage is more dangerous if accidentally touched or if there is an accidental short circuit.
5. Two similarly charged bodies are kept 5 cm apart in air. If the second body is shifted away from the first by another 5 cm, their force of repulsion will be
reduced to one-fourth
Answer (d). F = kQ1Q2/d2
6. The resistance of a wire is 10Ω. If it is stretched ten times, the resistance will be
Answer (d). If a wire is stretched uniformly to n-times its original length, it's
resistance changes by a factor of n2
7. A house, served by a 220 V supply line, is protected by a 9 A fuse. What is the maximum number of 60 watt bulbs that can be turned on in parallel?
Answer (c). Each bulb consumes 60/220 amperes of current. Hence in 9 ÷ 60/220 gives us 33.
8. Two metallic wires A and B are of same material and have equal length. If the cross-sectional area of B is double that of A, then which one among the following is the electrical resistance of B?
Twice that of A
4 times that of A
1/4 that of A
1/2 that of A
9. Three resistance coils of 1 Ω, 2 Ω and 3 Ω are connected in series. If the combination is connected to a battery of 9 V, what is the potential drop across the resistance coil of 3 Ω ?
Answer (c). Total resistance is 6 Ω and thus the current through the circuit is 9/6 = 1.5 A. Voltage drop across e Ω resistance is 3 x 1.5 = 4.5 v.
10. An electric lamp of 100 watt is used for 10 hours per day. The ‘units’ of energy consumed in one day by the lamp is
Answer (a). On unit of energy (1 kilowatt hour) is consumed when a 1000 watt appliance is kept 'ON' for 1 hour. Thus 100 watt bulb for 10 hours consumes 100 x 10 = 1000 wH or 1 kwH of energy.
11. An electric iron of resistance 20 W takes a current of 5 A. The heat developed in joules in 30 s is
Answer (c). Heat produced = I2Rt = 52 x 20 x 30 = 15000 joules or 15 kJ.
12. Kilowatt-hour is the unit of
13. Two copper wires A and B of length L and 2L respectively, have the same area of cross-section. The ratio of the resistivity of wire A to the resistivity of wire B is
14. If the electrical resistance of a typical substance suddenly drops to zero, then the substance is called
15. The material used for electric fuse is an alloy of tin and lead. This alloy should have
high specific resistance and low melting point
low specific resistance and high melting point
low specific resistance and low melting point
high specific resistance and high melting point
16. Capacity of a parallel plate condenser can be doubled by:
doubling the areas of the plates
doubling the distance of separation between the plates
reducing the distance of separation between the plates to half the original separation
doubling both the areas of the plates and the distance of separation between the plates
Select the correct answer using the code given below:
1 and 4
1 and 3
2 and 3
Answer (c). The capacity can be doubled by EITHER doubling the are of the plates OR halving the distance between the plates. If you do both the capacitance would be quadrupled.
17. If two conducting spheres are separately charged and then brought in contact:
the total energy of the two spheres is conserved
the total charge on the spheres is conserved
both the total energy and charge are conserved
the final potential is always the mean of the original potential of the two spheres
18. Two pieces of metallic wire having equal length and equal volume placed in air have different resistances. The two wires must:
have different cross sections
have different temperatures
be of different materials
be of same density
19. If a heater coil is cut into two equal parts and only one part is used in the heater, the heat generated will be:
20. A hollow metal ball carrying an electric charge produces no electric field at points:
outside the sphere
on its surface
inside the sphere
only at the centre
21. Microwave oven consumes less power due to:
small frequency of radiation
short wavelength of radiation
large frequency as well as wavelength of radiation
small frequency as well as wavelength of radiation
22. How many sixty watt (60 W) bulbs may be safely used in a 240-V supply with 4-ampere fuse?
Answer (d). Each bulb draws 1/4 amperes of current, hence for a 4 ampere fuse the maximum number of bulbs would be 4 ÷ 1/4 = 16.
23. The effective resistance of three equal resistances, each of resistance r, connected in parallel, is
24. The specific resistance of a conducting wire depends upon
length of the wire, area of cross-section of the wire and material of the wire
length of the wire and area of cross-section of the wire but not on the material of the wire
material of the wire only but neither on the length of the wire nor on the area of cross-section of the wire
length of the wire only but neither on the area of cross-section of the wire nor on the material of the wire
25. Net charge in a current-carrying conductor is
either positive or negative
26. Which one of the following is the resistance that must be placed parallel with 12 Ω resistance to obtain a combined resistance of 4 Ω?