#### Current Electricity Important Questions

12th Standard EM

Reg.No. :
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Physics

Time : 01:00:00 Hrs
Total Marks : 50
10 x 1 = 10
1. A toaster operating at 240 V has a resistance of 120 Ω. Th e power is

(a)

400 W

(b)

2 W

(c)

480 W

(d)

240 W

2. A carbon resistor of (47 ± 4.7 ) k Ω to be marked with rings of diff erent colours for its identifi cation. Th e colour code sequence will be

(a)

Yellow – Green – Violet – Gold

(b)

Yellow – Violet – Orange – Silver

(c)

Violet – Yellow – Orange – Silver

(d)

Green – Orange – Violet - Gold

3. Two wires of A and B with circular cross section made up of the same material with equal lengths. Suppose RA = 3 RB, then what is the ratio of radius of wire A to that of B?

(a)

3

(b)

$\sqrt3$

(c)

$\frac{1}{\sqrt3}$

(d)

$\frac{1}{3}$

4. A wire connected to a power supply of 230 V has power dissipation P1. Suppose the wire is cut into two equal pieces and connected parallel to the same power supply. In this case power dissipation is P2. The ratio $\frac{P_2}{P_1}$ is

(a)

1

(b)

2

(c)

3

(d)

4

5. When 'n' resistors of equal resistance (R) are connected in series and in parallel respectively,then the ratio of their effective resistance is

(a)

1: n2

(b)

n2: 1

(c)

n: 1

(d)

1: n

6. Which of the following has negative temperature coefficient of resistance?

(a)

copper

(b)

tungsten

(c)

carbon

(d)

silver

7. The temperature co-efficient of resistance for alloys is

(a)

low

(b)

very low

(c)

high

(d)

very high

8. Which of the following material has the highest specific resistance?

(a)

rubber

(b)

silver

(c)

germanium

(d)

glass

9. Temperature co-effieient of resistance for metals is

(a)

constant

(b)

positive

(c)

zero

(d)

negative

10. An electron gun in a TV shoots out a beam of electrons. The obeam current is lOll A. The charge that strikes the screen in I minute is

(a)

$+600\mu C$

(b)

$-600\mu C$

(c)

$+10\mu C$

(d)

$-10\mu C$

11. 5 x 2 = 10
12. Why current is a scalar?

13. Define electrical resistivity

14. Define temperature coefficient of resistance.

15. Define current.

16. Define instantaneous current

17. 5 x 3 = 15
18. Compute the current in the wire if a charge of 120 C is flowing through a copper wire in 1 minute.

19. If an electric field of magnitude 570 N C-1, is applied in the copper wire, find the acceleration experienced by the electron.

20. A copper wire of cross-sectional area 0.5 mm2 carries a current of 0.2 A. If the free electron density of copper is 8.4 × 1028 m-3 then compute the drift velocity of free electrons.

21. Derive an expression of drift velocity and write the relation between drift velocity and mobility.

22. How does one can understand the temperature dependence of resistivity of a conductor?

23. 3 x 5 = 15
24. A battery of voltage V is connected to 30 W bulb and 60 W bulb as shown in the figure. (a) Identify brightest bulb (b) which bulb has greater resistance?
(c) Suppose the two bulbs are connected in series, which bulb will glow brighter?

25. Two electric bulbs marked 20 W – 220 V and 100 W – 220 V are connected in series to 440 V supply. Which bulb will be fused?

26. How will you represent a resistor of 3700$\Omega$ ± 10 by colour code?