12th physics chapter 3 objective questions in English

1. A cell of e.m.f. 1.5 V is connected with an ammeter of resistance 0.05 Ω. If the current in the circuit is 2.0 A, the internal resistance of the cell is-

(Α) 1.0 Ω

(Β) 0.9 Ω

(C) 0.8 Ω

(D) 0.7 Ω

2. The number of electrons that constitute 1 A of current is :

(A) 6.25 × 10¹⁶

(B) 6.25 × 10¹⁷

(C) 6.25 × 10¹⁸

(D) 6.25 × 10¹⁹

3. The length of a conductor is halved. Its resistance will be :

(A) halved

(B) doubled

(C) unchanged

(D) quadrupled

4. Siemen is the unit of :

(A) resistance

(B) conductance

(C) specific conductance

(D) None of these

5. Kirchhoff’s first and second laws for electrical circuits are consequences of :

(A) conservation of energy

(B) conservation of electrical charge and energy respectively

(C) conservation of electric charge

(D) neither conservation of energy nor electric charge

6. A 5 A fuse wire can with stand a maximum power of 1 W in circuit. The resistance of the fuse wire is :

(A) 0.2 Ω

(B) 5 Ω

(C) 0.4 Ω

(D) 0.04 Ω

7. Ohm’s law is valid when the temperature of conductor is :

(A) very low

(B) very high

(C) varying

(D) constant

8. Emf is measured in :

(A) joule

(B) joule/coulomb

(C) joule-coulombs

(D) joule/coulomb/metre

9. 1 kilowatt hour is commonly known as :

(A) 1unit

(B) 1 faraday

(C) 1 curie

(D) None of these

10. How many joules are equal to I kWh ?

(A) 3.6 × 10⁴

(B) 3.6 × 10⁵

(C) 3.6 × 10⁶

(D) None of these

11. The temperature coefficient of resistance is expressed in :

(A) °C

(B) °C^-1

(C) m°C^-1

(D) None of these

12. Copper wire is used as connecting wire because :

(A) copper has high electrical resistivity

(B) copper has low electrical resistivity

(C) copper has low electrical conductivity

(D) copper has high value of elasticity

13. The specific resistance of a conductor increases with :

(A) increase in temperature

(B) increase in cross-sectional area

(C) decrease in length

(D) decrease in cross-sectional area

14. Which of the following has a negative temperature coefficient of resistance ?

(A) Tungsten

(B) Carbon

(C) Nichrome

(D) Platinum

15. Two bulbs 25 W, 220 V and 100 W, 220 V are given. Which has higher resistance?

(A) 25 W

(B) 100 W

(C) both bulbs have equal resistance

(D) resistance of bulbs can not be compared

16. The electrical resistance of a healthy man is –

(Α) 50,000 Ω

(B) 10,000

(C) 1,000 Ω

(D) 10 Ω

17. The peak voltage of an A.C. is 440 volt. Its virtual voltage is –

(A) 220 V

(B) 440 V

(C) 220 √2 V

(D) 440 √2 V

18. A current of 10 ampere flows in a wire for 10 sec. If potential difference across the wire is 15 volt, the work done will be –

(A) 150 J

(B) 75 J

(C) 1500 J

(D) 750 J

19. A current flows in a wire of resistance 5Ω having potential difference 7 volt for 20 minutes. The heat produced is –

(A) 140 cal

(B) 280 cal

(C) 700 cal

(D) 2800 cal.

20. The algebraic sum of all currents meeting at any point in an electrical circuit is –

(A) infinite

(B) positive

(C) zero

(D) negative

21. Power of electric circuit is –

(A) V.R

(B) V².R

(C) V²/R

(D) V².R.I

22. Electron-volt (eV) is the measure of

(A) charge

(B) potential

(C) current

(D) energy

23. With the increase of temperature, the resistance of a semiconductor –

(A) increases

(B) decreases

(C) sometimes increases and sometimes decreases

(D) remains unchanged

24. The ratio of peak value and r.m.s. value of ac is

(A) 2

(B) √2

(C) 1/√2

(D) √2/1

25. The torque acting on electric dipole of dipole moment placed in electric field of intensity is –

(A)

(B)

(C)

(D)

26. When an ammeter is shunted, its measuring range –

(A) increases

(B) decreases

(C) remains constant

(D) none of these

27. Ampere-hour is unit of –

(A) Power

(B) Charge

(C) Energy

(D) Potential difference

28. Dimension of electromotive force (e.m.f.) is –

(A) ML²T²

(B) ML²T^-3I^-1

(C) MLT^-2

(D) ML²T^-3I^-3

29. Hot wire ammeter measures –

(A) peak value of ac

(B) average value of ac

(C) r.m.s. ac

(D) none of these

30. Two cells of emfe, and 2, internal resistance r, and r₂, connected in parallel. The equivalent emf of the combination is –

(A) ∈₁r₁+∈₂r₂/r₁+r₂

(B) ∈₁r₂+∈₂r₁/r₁+r₂

(C) √∈₁+∈₂

(D) ∈₁+∈₂/2

31. Which element is used in electric heater ?

(A) Copper

(B) Platinum

(C) Tungsten

(D) Nichrome

32. Absorbed electrical energy is –

(A) Proportional to the potential difference

(B) Inversely proportional to the potential difference

(C) Proportional to the square of the potential difference

(D) None of these

33. Wheat stone’s bridge is used in measuring –

(A) High resistance

(B) Low resistance

(C) Both high and low resistance

(D) Potential difference

34. The specific resistance of a conductor increases with –

(A) increase of temperature

(B) increase of cross-sectional area

(C) decrease in length

(D) Decrease of cross-sectional area

35. The Drift velocity(V_d ) and applied electric field (E)of a conductor are related as

(A) V_d √E

(B) V_d E

(C) V_d E²

(D) V_d = constant

36. The ratio of root mean square (rms) value and peak value of an alternating current is –

(A) √2

(B) 1/√2

(C) 1/2

(D) 2√2

37. With the increase of temperature the resistivity of semiconductor –

(A) increases

(B) decreases

(C) remains constant

(D) becomes zero

38. When two bulbs of power 60 W and 40 W are connected in series, then the power of their combination will be –

(A) 100 W

(B) 2400 W

(C) 30 W

(D) 24 W

39. The resistance of Ammeter is –

(A) small

(B) large

(C) very small

(D) very large

40. At constant potential difference, the resistance of any electric circuit is halved, the value of heat produced will be –

(A) half

(B) double

(C) four times

(D) same

41. The value of red colour in colour code of carbon resistance is –

(A) 0

(B) 1

(C) 2

(D) 3

42. Which of the following has unit Volt/metre ?

(A) Electric flux

(B) Electric potential

(C) Electric capacity

(D) Electric field

43. The heat produced in a conductor of resistance R due to flow of current I for time t is –

(A) I.R.t

(B) I.R².t

(C) I².R.t

(D) I².R².t

44. Which of the following is correct for resistivity of a material ?

(A) ρ = RA/L

(B) ρ = L/RA

(C) ρ = RL/A

(D) ρ = R.L.A

45. Which of the following is the best conductor of electricity?

(A) Silver

(B) Copper

(C) Gold

(D) Zinc

46. One ampere is equal to –

(A) 1 coulomb/1second

(B) 1 coulomb x 1 second

(C) 1 volt x 1 ohm

(D) 1ohm/1volt

47. Unit of electromotive force is –

(A) newton

(B) joule

(C) volt

(D) newton/ampere

48. Electric-potential is equal to –

(A) q/W

(B) W/q

(C) Wq

(D) √Wq