Which of the following factors affects the resistance of a conductor?
(A) Length of the conductor
(B) Cross-sectional area of the conductor
(C) Temperature of the conductor
(D) All of the above
Answer: (D) All of the above
Explanation:
Resistance (R) is given by the formula:
R = ρ L / A
Where:
L = Length of the conductor (Directly proportional)
A = Cross-sectional area (Inversely proportional)
ρ = Resistivity of the material (Varies with temperature)
Temperature affects resistivity, which in turn alters the resistance.
A wire of resistance 10 Ω is stretched to double its length. What will be its new resistance?
(A) 20 Ω
(B) 40 Ω
(C) 5 Ω
(D) 10 Ω
Answer: (B) 40 Ω
Explanation: When a wire is stretched to double its length, the new length becomes 2L and the area becomes half A / 2, leading to an increase in resistance by a factor of 4.
Rnew = ρ 2L / A / 2 = 4R
Rnew = 4 × 10Ω = 40Ω
Kirchhoff’s First Law is based on which principle?
(A) Conservation of energy
(B) Conservation of momentum
(C) Conservation of charge
(D) Conservation of mass
Answer: (C) Conservation of charge
Explanation: Kirchhoff’s First Law (KCL) states that the sum of currents entering a junction equals the sum of currents leaving the junction. This is derived from the conservation of electric charge.
Iin = Iout
The internal resistance of a cell is defined as:
(A) Resistance between the terminals of the cell
(B) Resistance of the electrolyte inside the cell
(C) Resistance offered by the external circuit
(D) Resistance of the connecting wires
Answer: (B) Resistance of the electrolyte inside the cell
Explanation:
Internal resistance arises due to the resistance offered by the electrolyte and electrodes inside the cell.
The terminal voltage of a cell is given by:
V = E − Ir
Where:
E is the EMF of the cell
r is the internal resistance
I is the current
What is the equivalent resistance when three resistors of 6 Ω, 3 Ω, and 2 Ω are connected in parallel?
(A) 1 Ω
(B) 2 Ω
(C) 3 Ω
(D) 4 Ω
Answer: (A) 1 Ω
Explanation:
For parallel combination:
1 / Req = 1 / 6 + 1 / 3 +1/ 2
1 / Req1=61+31+21 1 / Req = 1 + 2 + 3 / 6 = 6 / 6=1
Req = 1Ω
A 100 W, 200 V bulb is connected to a 100 V supply. What will be the power consumed?
(A) 100 W
(B) 50 W
(C) 25 W
(D) 75 W
Answer: (C) 25 W
Explanation:
Resistance of the bulb:
R = V2 / P=2002 /100 = 400Ω
Power consumed at 100 V:
P′ = V′2 / R = 1002 / 400 =10000 / 400 = 25W
Drift velocity is defined as:
(A) Speed of electrons in a conductor
(B) Net velocity acquired by electrons due to applied electric field
(C) Average speed of electrons due to thermal agitation
(D) Speed of current through a conductor
Answer: (B) Net velocity acquired by electrons due to applied electric field
Explanation:
Drift velocity is the average velocity gained by free electrons in a conductor under the influence of an electric field.
Formula:
vd = I / nAe
Where:
I is current
n is electron density
A is cross-sectional area
e is the charge of the electron
A battery of EMF 12 V and internal resistance 1 Ω is connected to a resistor of 5 Ω. What is the terminal voltage?
(A) 10 V
(B) 11 V
(C) 12 V
(D) 9 V
Answer: (B) 11 V
Explanation:
Current in the circuit:
I = E / R + r = 12 / 5 + 1 = 2A
Terminal voltage:
V = E – Ir = 12 − (2×1) = 12−2 =11V
If the length of a wire is doubled and its radius is halved, how will its resistance change?
(A) Remains same
(B) Becomes 4 times
(C) Becomes 8 times
(D) Becomes 2 times
Answer: (C) Becomes 8 times
Explanation:
Resistance is given by:
R = ρL / A
New length = 2L, New radius = r / 2, New area = π(r/2)2 = πr2 / 4
New resistance:
R′ = ρ 2L / A/4 = 8R
Which physical quantity remains constant in a series circuit?
(A) Current
(B) Voltage
(C) Resistance
(D) Power
Answer: (A) Current
Explanation:
In a series circuit, the same current flows through all components, while the voltage divides across them.
The unit of resistivity is:
(A) Ohm-meter
(B) Ohm per meter
(C) Siemens per meter
(D) Ampere-meter
Answer: (A) Ohm-meter
Explanation:
Resistivity (ρ) is given by:
Ρ = R A / L
Its unit is Ohm-meter (Ω⋅m).
A current of 3 A flows through a conductor for 2 minutes. How much charge passes through it?
(A) 360 C
(B) 6 C
(C) 60 C
(D) 180 C
Answer: (D) 180 C
Explanation:
Charge:
Q = I × t = 3 × 2 × 60 = 180 C
In a metallic conductor, what happens when the temperature increases?
(A) Resistance decreases
(B) Resistance increases
(C) No change in resistance
(D) Conductivity increases
Answer: (B) Resistance increases
Explanation: As temperature increases, the vibrations of atoms increase, obstructing the movement of electrons and thus increasing the resistance.
Which of the following materials has a negative temperature coefficient of resistance?
(A) Copper
(B) Silver
(C) Silicon
(D) Aluminum
Answer: (C) Silicon
Explanation: Semiconductors like silicon and germanium exhibit a negative temperature coefficient of resistance, meaning their resistance decreases with an increase in temperature.
The drift velocity of electrons in a conductor is directly proportional to:
(A) Cross-sectional area
(B) Electric field applied
(C) Temperature
(D) Length of the conductor
Answer: (B) Electric field applied
Explanation:
Drift velocity (vd) is given by:
vd = eEτ / m
Where:
E is the applied electric field, directly affecting the drift velocity.
Which device is used to measure electric current?
(A) Voltmeter
(B) Ammeter
(C) Galvanometer
(D) Rheostat
Answer: (B) Ammeter
Explanation:
An ammeter is connected in series with a circuit to measure electric current.
What is the value of the current if 120 C of charge passes through a conductor in 40 seconds?
(A) 3 A
(B) 2 A
(C) 4 A
(D) 1.5 A
Answer: (A) 3 A
Explanation:
I = Q / t = 120 / 40 = 3 A
The resistance of a conductor is inversely proportional to:
(A) Length
(B) Resistivity
(C) Cross-sectional area
(D) Temperature
Answer: (C) Cross-sectional area
Explanation:
Resistance is given by:
R = ρL / A
It decreases as the cross-sectional area increases.
Which law states that the current through a conductor is directly proportional to the potential difference across it?
(A) Ohm’s Law
(B) Faraday’s Law
(C) Ampere’s Law
(D) Coulomb’s Law
Answer: (A) Ohm’s Law
Explanation:
Ohm’s Law:
V = IR
Where:
V is the voltage,
I is the current,
R is the resistance.
A potentiometer works on the principle of: