Chapter summary — Current Electricity
This chapter deals with electric current in conductors — drift of electrons, current density, Ohm's law, resistivity and conductivity, temperature dependence of resistance, series and parallel circuits, Kirchhoff's rules, meters (ammeter, voltmeter), cells and internal resistance, EMF, principle of potentiometer, Wheatstone bridge and meter bridge, power and Joule heating. Key formulas and typical circuit problems are essential.
Revision tips: Memorize relations I=neAv_d, J=σE, R=ρL/A, power P=VI=I²R=V²/R, and practice Kirchhoff + potentiometer problems.
1. Electric current is defined as:
A) Rate of flow of electric charge ✅
B) Flow of electrons only
C) Flow of protons
D) Number of electrons
2. SI unit of current is:
A) Volt
B) Ampere (A) ✅
C) Ohm
D) Coulomb
3. Ohm's law states that:
A) V ∝ I²
B) V ∝ I (at constant temperature) ✅
C) V ∝ 1/I
D) I ∝ R
4. Resistivity (ρ) of a material is defined as:
A) R·A/L ✅
B) R·L/A
C) R·A·L
D) R·L²/A
5. The resistance of a conductor is directly proportional to:
A) Length ✅
B) Cross-sectional area
C) Temperature only
D) Resistivity inversely
6. For two resistors in series, the equivalent resistance is:
A) Sum of resistances (R1+R2) ✅
B) Product/sum
C) Reciprocal of sum
D) Zero
7. For two resistors in parallel, the equivalent resistance is:
A) R1+R2
B) R1·R2/(R1+R2) ✅
C) (R1+R2)/R1·R2
D) R1·R2
8. Current density J is related to electric field E by:
A) J=E/σ
B) J=σE ✅
C) J=ρE
D) J=E²
9. Drift velocity v_d is proportional to:
A) Number density of electrons
B) Electric field (E) ✅
C) Cross-sectional area
D) Temperature only
10. Ohmic conductors obey Ohm's law because:
A) Resistance decreases with voltage
B) V/I is constant at given temperature ✅
C) Current independent of voltage
D) Resistivity is zero
11. The unit of resistivity is:
A) Ohm
B) Ohm·m ✅
C) Siemens
D) Ampere/m
12. Specific conductivity is the reciprocal of:
A) Resistance
B) Resistivity ✅
C) Mobility
D) Drift velocity
13. Kirchoff's first law corresponds to which conservation law?
A) Conservation of charge ✅
B) Conservation of energy
C) Conservation of mass
D) Conservation of momentum
14. Kirchhoff's second law corresponds to which conservation law?
A) Charge
B) Energy (sum of emf = sum of potential drops) ✅
C) Mass
D) Momentum
15. Internal resistance of a cell causes:
A) Increase of terminal voltage under load
B) Terminal voltage decreases under load ✅
C) EMF to increase
D) No change
16. The terminal voltage V of a cell with EMF ε and internal resistance r when current I is drawn is:
A) V=ε+Ir
B) V=ε−Ir ✅
C) V=Ir−ε
D) V=ε·Ir
17. A potentiometer is used to measure:
A) Emf of a cell accurately ✅
B) Resistance only
C) Current only
D) Capacitance
18. In a potentiometer, no current flows through the test cell when the balancing length is found because:
A) It is short-circuited
B) Potential difference across it is zero (balance condition) ✅
C) Internal resistance infinite
D) EMF zero
19. Wheatstone bridge is used to measure:
A) Unknown resistance ✅
B) EMF
C) Current density
D) Temperature
20. Meter bridge is based on which principle?
A) Ohm's law only
B) Wheatstone bridge principle ✅
C) Potentiometer principle
D) Kirchhoff's loops
21. Power dissipated in a resistor is given by:
A) P=VI=I²R=V²/R ✅
B) P=V+I
C) P=IR/V
D) P=I/R
22. Joule's law of heating states that heat produced is proportional to:
A) I²Rt ✅
B) IRt
C) Vt
D) It
23. Superconductivity is characterized by:
A) Infinite resistance
B) Zero electrical resistance below critical temperature ✅
C) Constant resistivity
D) Negative current
24. In the expression R=ρL/A, if area is doubled, resistance becomes:
A) Half ✅
B) Double
C) Same
D) Quadruple
25. A material with negative temperature coefficient of resistance means:
A) Resistance decreases with rise in temperature ✅
B) Resistance increases with temperature
C) Resistance independent of temperature
D) Resistance infinite
26. The emf of a cell is equal to:
A) Work done per unit charge in moving charge across the cell ✅
B) Terminal voltage under load
C) Internal resistance
D) Power
27. The SI unit of resistivity is:
A) Ohm
B) Ohm·meter (Ω·m) ✅
C) Siemens
D) Ampere/meter
28. The drift velocity of electrons in a conductor is typically:
A) Very large (~10^6 m/s)
B) Very small (~10^-4 to 10^-3 m/s) ✅
C) Zero
D) Infinite
29. Which instrument has low resistance and is connected in series to measure current?
A) Voltmeter
B) Ammeter ✅
C) Galvanometer in open circuit
D) Potentiometer
30. Which instrument has high resistance and is connected in parallel to measure potential difference?
A) Ammeter
B) Voltmeter ✅
C) Galvanometer in series
D) Rheostat
31. For a series circuit, current is:
A) Same through all components ✅
B) Different through each
C) Zero
D) Inversely proportional to voltage
32. For a parallel circuit, potential difference across each branch is:
A) Same ✅
B) Different
C) Zero
D) Equal to total current
33. When cells of emf ε and internal resistance r are connected in series, total emf and internal resistance are:
A) emf = nε, r = nr ✅
B) emf = ε/n, r = r/n
C) emf = nε, r = r/n
D) emf = ε, r = nr
34. The metre bridge uses a uniform wire of length:
A) 1 meter ✅
B) 10 cm
C) 2 meters
D) Variable
35. In potentiometer experiment, balancing length is directly proportional to:
A) Emf of the cell ✅
B) Internal resistance
C) Current through driver only
D) Temperature
36. Specific conductance (conductivity) has units:
A) Ω·m
B) S·m^-1 (Siemens per meter) ✅
C) Ampere
D) Volt
37. A material with very low resistivity is called:
A) Conductor ✅
B) Insulator
C) Semiconductor
D) Superconductor
38. Which of the following is used to increase the range of an ammeter?
A) Use of a multiplier resistor
B) Use of a shunt resistor ✅
C) Decrease resistance
D) Increase emf
39. Which of the following is used to increase the range of a voltmeter?
A) Use of a series high resistance (multiplier) ✅
B) Shunt resistor
C) Short circuiting
D) Decreasing emf
40. The SI unit of current density is:
A) A
B) A·m^-2 ✅
C) S·m^-1
D) Ω·m
41. An electron gains kinetic energy when it moves through a potential difference V given by:
A) eV ✅
B) e/V
C) V/e
D) e+V
42. Thermistors have ______ temperature coefficient of resistance.
A) Positive (PTC)
B) Can be PTC or NTC, commonly NTC ✅
C) Zero
D) Infinite
43. The SI unit of resistivity ρ is:
A) Ω/m
B) Ω·m ✅
C) S·m^-1
D) V/A
44. In a circuit, if two identical bulbs are connected in series and then in parallel, which statement is true?
A) In series they glow brighter
B) In parallel they glow brighter ✅
C) Brightness same
D) They do not glow
45. Which law gives relation between emf, current and internal resistance?
A) ε = V + Ir ✅
B) ε = V − Ir
C) V = Ir
D) ε = Ir/V
46. Charge Q passing through a conductor in time t with current I is:
A) Q=It ✅
B) Q=I/t
C) Q=I+ t
D) Q=I−t
47. The mobility μ of charge carriers is related to drift velocity by:
A) v_d = μE ✅
B) v_d = μ/I
C) μ = v_d/I
D) μ = E/v_d
48. Which of the following is true for ideal potentiometer?
A) It draws current from the cell under test ✅
B) No current flows through the test cell when balanced ✅
C) It changes emf of test cell
D) It measures resistance directly
49. In a galvanometer, sensitivity is increased by:
A) Decreasing number of turns
B) Increasing number of turns and torque constant ✅
C) Decreasing magnetic field
D) Increasing moment of inertia
50. Which of these expressions gives conductance G of a conductor?
A) G = 1/ρ
B) G = σA/L (where σ = 1/ρ) ✅
C) G = ρL/A
D) G = R·L/A