#### 12th Standard Physics English Medium Current Electricity Reduced Syllabus Important Questions 2021

12th Standard

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Physics

Time : 01:00:00 Hrs
Total Marks : 105
Multiple Choice Questions
15 x 1 = 15
1. There is a current of 1.0 A in the circuit shown below. What is the resistance of P ?

(a)

1.5 Ω

(b)

2.5 Ω

(c)

3.5 Ω

(d)

4.5 Ω

2. 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

3. An unknown resistance is connected in parallel with a 15$\Omega$ resistance and a 12V battery. What is the value of the unknown resistance if the current in the circuit is 2A?

(a)

$10\Omega$

(b)

$20\Omega$

(c)

$30\Omega$

(d)

$40\Omega$

4. Kirchoff's I law i.e, $\Sigma i=0$ at a junction, deals with the conservation of

(a)

charge

(b)

energy

(c)

momentum

(d)

angular momentum

5. Resistance increases with increases in temperature for

(a)

conductor

(b)

semiconductors

(c)

insulators

(d)

superconductor

6. Joules's heating effect is desirable in

(a)

AC dynamo

(b)

DC dynamo

(c)

water heater

(d)

transformer

7. The sensitivity of a potentiometer can be increased by

(a)

decreasing the length of potentiometer wire

(b)

increasing the length of potentiometer wire

(c)

increasing the emf of the cell used in primary circuit

(d)

all the above

8. Two identical resistors are connected in parallel then connected in series. The effective resistance are in the ratio

(a)

1:2

(b)

2:1

(c)

1:4

(d)

4:1

9. A resistance of a metal wire of length AB is 2$\Omega$. Another wire of length PQ of the same metal with twice the diameter of the wire AB is found to have the same resistance of2$\Omega$. What is the length of PQ?

(a)

4 AB

(b)

2 AB

(c)

1AB

(d)

6 AB

10. When a current of 5 A flows through a conductor of resistance 3 $\Omega$ the loss of power due to joule heating effect is_________

(a)

75 W

(b)

25 W

(c)

70.7 W

(d)

45 W

11. When three resistors are connected in parallel then the value of the effective resistance is________

(a)

less than or equal to individual resistance

(b)

greater than or equal to individual resistance

(c)

less than the individual resistance

(d)

greater than the individual resistance

12. The algebraic sum of the currents meeting at any junction in the circuit is_______

(a)

infinity

(b)

negative value

(c)

2A

(d)

zero

13. Kirchhoff's law is applicable only for__________

(a)

simple circuits

(b)

primary circuits

(c)

complicated circuits

(d)

secondary circuits

14. Kirchhoff's I law is a consequence of__________

(a)

law of conservation of energy

(b)

law of conservation of charges

(c)

law of conservation of currents

(d)

law of conservation of voltages

15. In the case of Wheatstone)s Bridge) the bridge balance condition will be obtained only when____

(a)

the current through the galvanometer is maximum

(b)

the current through the galvanometer is minimum

(c)

the current through the galvanometer is zero

(d)

the current through the galvanometer is infinity

16. 2 Marks
10 x 2 = 20
17. Define temperature coefficient of resistance.

18. What is Seebeck effect?

19. What is Peltier effect?

20. Define resistance

21. Define the term electric power and circuit its SI unit.

22. What is (i) thermoelectric current
(Ii) thermocouple.

23. When resistors are connected in series. the effective resistance is increased. Why?

24. When resistors are connected in parallel the effectiveresistance is reduced. Why

25. Plot a graph showing the variation of circuit I various resistance R connected to a cell of emf E and internal resistance r.

26. Why are connecting resistors in a metrebridge made of thick copper strips?

27. 3 Marks
10 x 3 = 30
28. Compute the current in the wire if a charge of 120 C is flowing through a copper wire in 1 minute.

29. Calculate the equivalent resistance in the following circuit and also find the current I, I1 and I2 in the given circuit.

30. Calculate the equivalent resistance between A and B in the given circuit.

31. Explain the equivalent resistance of a series and parallel resistor network

32. Explain the determination of the internal resistance of a cell using voltmeter.

33. What is meant by electromotive force?

34. Derive a relation between internal resisance and emf of a cell

35. In a circuit containing internal resistance r. Find the power delivered

36. Find the expression for the equivalent emf & internal resistance of the series combination of cells

37. Explain Peltier effect.

38. 5 Marks
8 x 5 = 40
39. From the given circuit,

Find
i) Equivalent emf of the combination
ii) Equivalent internal resistance
iii) Total current
iv) Potential difference across external resistance
v) Potential difference across each cell

40. The following figure shows a complex network of conductors which can be divided into two closed loops like ACE and ABC. Apply Kirchoff’s voltage rule.

41. Calculate the current that flows in the 1 Ω resistor in the following circuit.

42. In a Wheatstone’s bridge P = 100 Ω, Q = 1000 Ω and R = 40 Ω. If the galvanometer shows zero deflection, determine the value of S.

43. Three identical lamps each having a resistance R are connected to the battery of emf as shown in the figure.

Suddenly the switch S is closed. (a) Calculate the current in the circuit when S is open and closed (b) What happens to the intensities of the bulbs A,B and C. (c) Calculate the voltage across the three bulbs when S is open and closed (d) Calculate the power delivered to the circuit when S is opened and closed (e) Does the power delivered to the circuit decreases, increases or remain same?

44. Two cells each of 5V are connected in series across a 8 Ω resistor and three parallel resistors of 4 Ω, 6 Ω and 12 Ω. Draw a circuit diagram for the above arrangement. Calculate i) the current drawn from the cell (ii) current through each resistor

45. Calculate the effect internal resistance in series and parallel.

46. An aluminium wire of diameter 0.24 cm is connected in series to a copper wire of diameter 0.16 cm. The wires carry an electric current of 10 A. Determine the current density in aluminium wire.