Physics Chapter 7 Entry test MCQs
Topic 7
Current Electricity
1. Give the number of electrons passing through a wire per minute. The current flowing through it is 500mA.
a. 1.875 x 1020
b. 1.875 x 10^20
c. 6.875 x 10^20
d. 6.875 × 10^20
2. Kabir bought 5 new light bulbs of 50 W each in addition to the 7 bulbs he already had in his house which were also 50 W each. Calculate his electricity bill, if he keeps the new bulbs on for 5 hours and the older bulbs on only for 3 hours, and the cost of one unit of electricity is Rs. 60.
a. Rs.138
b. Rs. 136
c. Rs.139
d. Rs.137
3. Which one of the following is the practical unit of power?
a. Horse power (hp)
b. Watt (W)
c. Kilojoule (kJ)
d. Kilowatt hour (kWh)
4. An engine uses 30 A of current. The resistance offered is 15 ohms. Calculate the power consumed by the engine in horse power.
a. 17 hp
b. 18 hp
c. 13500 hp
d. 19 hp
5. A current of 3 A passes through an electric circuit for 5 minutes and does a work of 900J. What is the emf of the source?
a. 5V
b. 3V
c. 10V
d. 1V
6. A cooler of 1500 W, 200 volt and a fan of 500 W, 200 volts are to be used from a household supply. The rating of fuse to be used is
a. 7.5 A
b. 2.5 A
c. 10 A
d. 5.0 A
7. An electric current is passed through a circuit containing two wires of the same material, connected in parallel. If the lengths and radii of the wires are in the ratio of 4/3 and 2/3, then the ratio of the currents passing through the wire will be
a. 1/3
b. 3
c. 2
d. 8/9
8. Graph between V and I for non-ohmic devices
a. Usually not straight-line
b. Straight line
c. Sometime straight line
d. Always not straight line
9. The current in a resistor is 8.0 mA. What charge flows through the resistor in 0.020 s?
a. 1.6 mC
b. 0.16 mC
c. 0.40 mC
d. 4.0 mC
10. Which of the following statements is not true?
a. Ohm’s law is not applicable at very low and very high temperatures
b. Conductance is the reciprocal of resistance and is measured in siemens
c. Ohm’s law is not applicable to electron tubes, discharge tubes
d. Semiconductors diode are ohmic devices
11. Ohm’s law establishes a relation between
a. Charge and voltage
b. Current and voltage
c. Current and resistance
d. Resistance and voltage
12. For an ohmic conductor, doubling the voltage without changing the resistance will cause the current to
a. Remain unchanged
b. Decrease by a factor of 4
c. Increase by a factor of 2
d. Decrease by a factor of 2
13. Which equation is used to define resistance?
a. Potential difference current × resistance
b. Energy (current)2 x resistance × time
c. Resistivity = resistance area + length
d. Power = (current)2 × resistance
14. The charge of an electron is 1.6 x 10-19 (c) How many electrons strike the screen of a cathode ray tube each second when the beam current is 16 mA
a. 1017
b. 1019
c. 10-17
d. 10-19
15. The following four wires are made of the same material and are at the same temperature. Which one of them has highest electrical resistance
a. length=50 cm, diameter = 0.5 mm
b. length=100 cm, diameter =1 mm
c. length=300 cm, diameter=3 mm
d. length=200 cm, diameter = 2 mm
16. The resistance of a wire of uniform diameter d and length l is R. The resistance of another wire of the same material but diameter 2d and length 4l will be
a. R
b. 2R
c. R/2
d. R/2
17. When the length and area of cross-section both are doubled, then its resistance
a. Will be doubled
b. Will become half
c. Will become four times
d. Will remain the same
18. The example for non-ohmic resistance is
a. Carbon resistance
b. Copper wire
c. Tungston wire
d. Diode
19. A wire 100cm long and 2.0 mm diameter has a resistance of 0.7 ohm, the electrical resistivity of the material is
a. 2.2 x 10-6 ohm m
b. 4.4 x 10-6 ohm m
c. 0.22 x 10-6 ohm m
d. 1.1 x 10-6 ohm m
20. Which the following have the same temperature coefficient of resistivity?
a. iron and platinum
b. iron and silver
c. silver and gold
d. platinum and silver
21. When a wire is stretched double of is length, then its resistance will be
a. 2 R
b. 16 R
c. 8 R
d. 4 R
22. A wire of resistance R is cut into two equal parts, its resistance becomes R/2 what happens to resistivity:
a. Half
b. Double
c. One fourth
d. Same
23. A wire of resistance R is stretched four times its length uniformly. Its new resistance will be
a. R/4
b. 16 R
c. R/16
d. 4 R
24. The resistance of a wire is 1 2. Which of the following is new resistance if length of wire is doubled?
a. 1/2 Ω
b. ΖΩ
c. 1/4 Ω
d. 4 Ω
25. When Cu and Ge are cooled to – 150°C Then resistance of Cu——— and that of Ge———.
a. Increases, decreases
b. Increases, increases
c. Decreases, increases
d. Decreases, decreases