The EMF of a cell is 2V and its internal resistance is 0.5Ω. When connected to external resistance, the terminal voltage is 1.8V. The current in the circuit is:
Answer: A
E - I×r = V_terminal. 2 - I×0.5 = 1.8. I×0.5 = 0.2. I = 0.4A
Q.42Easy
Three identical cells, each of EMF 1.5V and internal resistance 1Ω, are connected in series. The total EMF and internal resistance are:
Answer: C
In series: Total EMF = 1.5 + 1.5 + 1.5 = 4.5V. Total internal resistance = 1 + 1 + 1 = 3Ω
Q.43Easy
A rheostat is used in a circuit to:
Answer: B
A rheostat is a variable resistor used to control and vary the current in a circuit
Q.44Medium
When a conductor is heated, its resistance increases because:
Answer: C
Heating increases atomic vibrations, leading to increased collisions between electrons and atoms, thus increasing resistance
Q.45Medium
A copper wire and an aluminum wire of same length and cross-sectional area carry the same current. Which has greater voltage drop?
Answer: B
Aluminum has higher resistivity than copper. Since V = I×R and resistivity differs, aluminum wire has greater voltage drop
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Q.46Easy
In a parallel combination of resistors, the voltage across each resistor is:
Answer: B
In parallel combination, all resistors are connected across same two points, hence voltage across each is same
Q.47Hard
A heating element of resistance R is connected to a battery of EMF E and internal resistance r. Maximum power is dissipated in R when:
Answer: B
By maximum power transfer theorem, maximum power is transferred to external load when load resistance equals internal resistance
Q.48Easy
In a circuit with a battery of 10V and total resistance 5Ω, the power dissipated is:
Answer: C
P = V²/R = (10)²/5 = 5100 = 20W
Q.49Medium
Two resistors of 4Ω and 6Ω are connected in series with a 10V battery. The current through the circuit and power dissipated are respectively:
Answer: C
Total R = 4 + 6 = 10Ω. I = V/R = 1010 = 1A. P = V×I = 10×1 = 10W
Q.50Easy
In a circuit, if the current increases when voltage increases, the resistance must:
Answer: C
From Ohm's law: I = V/R. If I increases with increasing V while R stays constant, then the relationship is proportional and follows Ohm's law
Q.51Medium
A wire of length L and cross-sectional area A has resistivity ρ. If the wire is stretched to double its length, what will be the new resistance?
Answer: C
When wire is stretched to 2L, area becomes A/2. New resistance = ρ(2L)/(A/2) = 4ρL/A = 4R
Q.52Easy
Which of the following materials has the lowest temperature coefficient of resistance?
Answer: B
Constantan (copper-nickel alloy) has the lowest temperature coefficient of resistance, making it ideal for standard resistors
Q.53Easy
In a Wheatstone bridge, if P/Q = R/S, then the galvanometer shows zero deflection. This condition is called:
Answer: C
Both balance condition and null point refer to the same situation where no current flows through the galvanometer
Q.54Medium
A battery with EMF E and internal resistance r is connected to an external resistance R. What is the terminal voltage?
Answer: B
Terminal voltage V = E - Ir, where I = E/(R+r), so V = E - E·r/(R+r) = ER/(R+r)
Q.55Easy
Five resistors each of 5Ω are connected in parallel. The equivalent resistance is:
Answer: C
For parallel: 1/R_eq = 5×(51) = 1, so R_eq = 1Ω
Q.56Medium
A potentiometer wire of length 100 cm has resistance 10Ω. A standard cell of EMF 1.5V is balanced at 40 cm. What is the EMF of an unknown cell if balanced at 65 cm?
Answer: C
By potentiometer principle: E₁/E₂ = l₁/l₂, so E₂ = 1.5 × (4065) = 2.4375V ≈ 2.4V
Q.57Easy
The specific resistance (resistivity) of a material depends on:
Answer: B
Resistivity is an intrinsic property dependent on the material's nature and temperature, not on the dimensions or electrical parameters
Q.58Medium
In a circuit, the current through a 10Ω resistor is 2A. If this resistor is replaced by 5Ω, and the rest of the circuit remains unchanged, the new current will be:
Answer: D
Current depends on both the resistor value and the rest of the circuit configuration (series/parallel). Without knowing the circuit configuration, it cannot be determined
Q.59Medium
A uniform wire of length L is cut into n equal parts. When connected in parallel, the equivalent resistance is:
Answer: A
Each part has resistance R/n. In parallel: 1/R_eq = n/(R/n) = n²/R, so R_eq = R/n²
Q.60Easy
The drift velocity of electrons in a conductor is of the order of:
Answer: B
Drift velocity is typically 10⁻⁴ to 10⁻³ m/s, much smaller than electron thermal velocity or speed of electrical signal
