Physics – Current Electricity
Class 12 Physics (Chapter 3) • 100 Multiple Choice Questions
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Question 1
What is the SI unit of electric current?
Correct Answer: Ampere (A)
Question 2
Electric current is a:
Correct Answer: Scalar quantity
Question 3
The relation between electric current (I) and drift velocity (v_d) is:
Correct Answer: I = n e A v_d
Question 4
Ohm's Law is expressed as:
Correct Answer: V = I R
Question 5
The SI unit of electrical resistivity is:
Correct Answer: Ohm-meter (Ω·m)
Question 6
Electrical conductivity (σ) is the reciprocal of:
Correct Answer: Resistivity
Question 7
The SI unit of electrical conductivity is:
Correct Answer: Siemens per meter (S/m) or (Ω·m)⁻¹
Question 8
Mobility (μ) of a charge carrier is defined as:
Correct Answer: Drift velocity per unit electric field (v_d / E)
Question 9
What is the SI unit of mobility?
Correct Answer: m² / (V·s)
Question 10
With an increase in temperature, the resistivity of metallic conductors:
Correct Answer: Increases
Question 11
With an increase in temperature, the resistivity of semiconductors:
Correct Answer: Decreases
Question 12
Kirchhoff's First Law (Current Law / KCL) is based on the conservation of:
Correct Answer: Charge
Question 13
Kirchhoff's Second Law (Voltage Law / KVL) is based on the conservation of:
Correct Answer: Energy
Question 14
The Wheatstone bridge is most sensitive when all four resistances are of the:
Correct Answer: Same order of magnitude
Question 15
The balance condition for a Wheatstone bridge with resistances P, Q, R, S is:
Correct Answer: P / Q = R / S
Question 16
Internal resistance (r) of a cell of emf E and terminal potential difference V when connected across external resistance R is given by:
Correct Answer: r = ((E - V) / V) * R
Question 17
Electromotive force (EMF) of a cell is:
Correct Answer: The potential difference across its terminals when no current is drawn
Question 18
When a cell is being charged, the terminal potential difference V and EMF E are related as:
Correct Answer: V = E + I r
Question 19
When a cell is discharging current into an external circuit, terminal potential V is:
Correct Answer: Less than EMF E (V = E - I r)
Question 20
Electrical power dissipated in a resistor of resistance R carrying current I is:
Correct Answer: P = I² R
Question 21
Commercial unit of electrical energy is:
Correct Answer: Kilowatt-hour (kWh)
Question 22
1 kWh is equal to how many Joules?
Correct Answer: 3.6 × 10⁶ J
Question 23
A potentiometer is preferred over a voltmeter for measuring EMF of a cell because:
Correct Answer: It draws no current from the cell at null point
Question 24
Sensitivity of a potentiometer can be increased by:
Correct Answer: Decreasing the potential gradient along the wire
Question 25
The drift velocity of free electrons in a conductor is typically of the order of:
Correct Answer: 10⁻⁴ m/s
Question 26
Relaxation time (τ) is defined as:
Correct Answer: Average time interval between successive collisions of electrons
Question 27
Resistivity in terms of relaxation time τ and electron density n is given by:
Correct Answer: ρ = m / (n e² τ)
Question 28
When a wire is stretched to double its length, its new resistance becomes:
Correct Answer: Four times (4R)
Question 29
Superconductors are materials that exhibit:
Correct Answer: Zero electrical resistance at very low temperatures
Question 30
The color code for carbon resistors uses bands. What does the fourth band indicate?
Correct Answer: Tolerance percentage
Question 31
If a carbon resistor has bands of colors Red, Red, Red, and Gold, its resistance value is:
Correct Answer: 2.2 kΩ ± 5%
Question 32
Gold band on a carbon resistor represents a tolerance of:
Correct Answer: ± 5%
Question 33
Silver band on a carbon resistor represents a tolerance of:
Correct Answer: ± 10%
Question 34
If there is no fourth band on a carbon resistor, the tolerance is assumed to be:
Correct Answer: ± 20%
Question 35
When n identical cells each of emf E and internal resistance r are connected in series, the total emf and internal resistance are:
Correct Answer: nE and n r
Question 36
When n identical cells each of emf E and internal resistance r are connected in parallel, the total emf and internal resistance are:
Correct Answer: E and r/n
Question 37
For maximum current from a mixed grouping of cells (m rows and n cells in each row), the condition is:
Correct Answer: External resistance R = (m · r) / n
Question 38
A meter bridge works on the principle of:
Correct Answer: Wheatstone bridge
Question 39
In a meter bridge, the null point is obtained at length l. The unknown resistance X is given by:
Correct Answer: X = R · ((100 - l) / l)
Question 40
The temperature coefficient of resistance (α) for most metals is:
Correct Answer: Positive
Question 41
Alloys like Manganin and Constantan have a temperature coefficient of resistance that is:
Correct Answer: Very small and nearly zero
Question 42
Why are Manganin and Constantan used for making standard resistance coils?
Correct Answer: Their resistance does not change much with temperature
Question 43
Joule's law of heating states that heat produced (H) in a resistor is proportional to:
Correct Answer: I² R t
Question 44
Which material is commonly used for electric heater elements (filaments)?
Correct Answer: Nichrome
Question 45
Why is Nichrome used as a heating element?
Correct Answer: High resistivity and high melting point
Question 46
An electric fuse wire should have:
Correct Answer: Low melting point and high resistivity
Question 47
Vector form of Ohm's Law is expressed as:
Correct Answer: J = σ E
Question 48
Current density J is defined as current per unit:
Correct Answer: Cross-sectional area normal to current
Question 49
What is the SI unit of current density?
Correct Answer: A / m²
Question 50
Current density is a:
Correct Answer: Vector quantity
Question 51
When resistors are connected in series, the equivalent resistance is:
Correct Answer: Greater than the largest individual resistance
Question 52
When resistors are connected in parallel, the equivalent resistance is:
Correct Answer: Less than the smallest individual resistance
Question 53
The drift velocity of electrons is directly proportional to:
Correct Answer: Applied electric field intensity
Question 54
Ohm's law is obeyed by:
Correct Answer: Metallic conductors at constant temperature
Question 55
Which of the following materials is non-ohmic?
Correct Answer: Diode / Semiconductor
Question 56
The dimensional formula of resistance (R) is:
Correct Answer: [M L² T⁻³ A⁻²]
Question 57
The dimensional formula of resistivity (ρ) is:
Correct Answer: [M L³ T⁻³ A⁻²]
Question 58
The terminal potential difference of a cell is equal to its EMF when:
Correct Answer: No current is drawn from the cell (Open circuit)
Question 59
Maximum power is transferred from a source of internal resistance r to an external load R when:
Correct Answer: R = r
Question 60
What is the efficiency of a cell when maximum power is delivered to the load?
Correct Answer: 50%
Question 61
Which of the following has negative temperature coefficient of resistance?
Correct Answer: Semiconductors and Insulators
Question 62
In a carbon resistor, the third band represents:
Correct Answer: Multiplier (power of 10)
Question 63
What is the color code digit for Black in carbon resistors?
Correct Answer: 0
Question 64
What is the color code digit for Brown in carbon resistors?
Correct Answer: 1
Question 65
What is the color code digit for Red in carbon resistors?
Correct Answer: 2
Question 66
What is the color code digit for Yellow in carbon resistors?
Correct Answer: 4
Question 67
What is the color code digit for Blue in carbon resistors?
Correct Answer: 6
Question 68
The internal resistance of an ideal voltmeter is:
Correct Answer: Infinite
Question 69
The internal resistance of an ideal ammeter is:
Correct Answer: Zero
Question 70
To convert a galvanometer into an ammeter, we connect a:
Correct Answer: Low resistance (shunt) in parallel
Question 71
To convert a galvanometer into a voltmeter, we connect a:
Correct Answer: High resistance in series
Question 72
Why is copper or aluminum used for transmission of electric power over long distances?
Correct Answer: They have very low resistivity
Question 73
Drift velocity v_d of electrons in a metal wire carrying current I is proportional to:
Correct Answer: Current I
Question 74
The reciprocal of resistance is called:
Correct Answer: Conductance
Question 75
What is the SI unit of electrical conductance?
Correct Answer: Siemens (S) or Ohm⁻¹ (mho)
Question 76
When a metallic conductor is heated, its resistance increases because:
Correct Answer: Frequency of collisions between electrons and ions increases
Question 77
The terminal potential difference V across a cell of EMF E and internal resistance r delivering current I is:
Correct Answer: V = E - I r
Question 78
In a potentiometer experiment, the null point is obtained when:
Correct Answer: The potential difference across the balancing wire length equals the EMF being measured
Question 79
Potential gradient (k) of a potentiometer wire is defined as:
Correct Answer: Potential drop per unit length of the wire (V / L)
Question 80
What is the SI unit of potential gradient?
Correct Answer: V / m
Question 81
Which instrument is best for comparing EMFs of two cells accurately?
Correct Answer: Potentiometer
Question 82
The drift speed of electrons depends on:
Correct Answer: Electric field and relaxation time
Question 83
When current flows through a conductor, heat is generated due to:
Correct Answer: Collisions of drifting electrons with lattice ions
Question 84
If the length of a wire is doubled and its cross-sectional area is also doubled, its resistance:
Correct Answer: Remains unchanged
Question 85
The resistivity of a material depends upon:
Correct Answer: Nature of the material and temperature
Question 86
In a balanced Wheatstone bridge, if the galvanometer and battery are interchanged, the galvanometer shows:
Correct Answer: No deflection (remains balanced)
Question 87
The drift speed of free electrons in a copper wire carrying 1 A current is roughly:
Correct Answer: 1 mm per second
Question 88
Why does a bulb glow almost instantaneously when the switch is turned on?
Correct Answer: Electric field sets up an electrical disturbance at the speed of light
Question 89
If the resistance of a circuit is halved while voltage remains constant, the power dissipated becomes:
Correct Answer: Doubled
Question 90
The total current entering a junction in a circuit is equal to the total current leaving the junction. This is:
Correct Answer: Kirchhoff's Current Law (KCL)
Question 91
The algebraic sum of changes in potential around any closed loop in a circuit is zero. This is:
Correct Answer: Kirchhoff's Voltage Law (KVL)
Question 92
Why is the bridge wire in a meter bridge usually made of Manganin or Constantan?
Correct Answer: Due to high resistivity and low temperature coefficient
Question 93
What is the color code for a resistor of value 47 kΩ ± 5%?
Correct Answer: Yellow, Violet, Orange, Gold
Question 94
If two identical resistors of resistance R are connected in parallel, the equivalent resistance is:
Correct Answer: R / 2
Question 95
The unit of electrical energy in terms of basic units is:
Correct Answer: Watt-second (W·s) or Joule (J)
Question 96
Which of the following factors affects the internal resistance of a cell?
Correct Answer: Distance between electrodes, area of electrodes, and concentration of electrolyte
Question 97
What is the dimensional formula of electric power?
Correct Answer: [M L² T⁻³]
Question 98
What happens to the current in a circuit if both resistance and voltage are doubled?
Correct Answer: Remains unchanged
Question 99
The drift velocity of electrons depends on the electric field E as:
Correct Answer: v_d ∝ E
Question 100
Which of the following describes the microscopic form of Ohm's law?
Correct Answer: J = σ E
