Circuits — Set 2
Physics · परिपथ · Questions 11–20 of 50
Heat produced in a resistor R by a current I in time t is given by which expression?
Correct Answer: A. H = I^2Rt
Joule’s law of heating gives H = I^2Rt for a resistor carrying current I for time t. More current produces much more heating because of the square term. The same result can also be written as H = V^2t/R when voltage is known.
What does the current rating of a fuse wire represent?
Correct Answer: A. Maximum safe current before it melts
A fuse rating is the maximum safe current it can carry without melting. If current exceeds this value, the fuse melts and breaks the circuit. Fuses protect wiring and devices from overheating due to overcurrent.
Two identical bulbs are connected in series to a battery. Compared to a single bulb, each bulb glows how?
Correct Answer: A. Dimmer than the single bulb
In series, the total resistance increases and the current becomes smaller, so each bulb is dimmer. Both bulbs carry the same reduced current in a series circuit. If the bulbs were connected in parallel, each would glow closer to normal brightness.
If the length of a uniform wire is doubled while keeping its area and material the same, what happens to its resistance?
Correct Answer: D. It becomes twice
Resistance is R = ρL/A, so doubling L makes R twice. Resistivity ρ depends on the material and temperature, not on size. Making a wire longer generally reduces current for the same applied voltage.
What is the SI unit of electrical resistivity?
Correct Answer: C. Ω·m
Resistivity is defined from R = ρL/A, so its SI unit is ohm meter, written Ω·m. It is a material property that indicates how strongly the material opposes current. Conductors have low resistivity while insulators have very high resistivity.
For most metallic conductors, how does resistance change when temperature increases?
Correct Answer: C. Resistance increases
For metals, resistance generally increases with temperature because lattice vibrations increase. This reduces the mean free path of electrons and increases collisions. Semiconductors usually show the opposite trend where resistance decreases with temperature.
In an RC charging circuit, the time constant τ corresponds to what change in capacitor voltage?
Correct Answer: C. It reaches about 63% of its final value
In RC charging, at time τ = RC the capacitor voltage reaches about 63% of its final value. The time constant sets how fast the capacitor charges or discharges. After about 5τ the capacitor is considered nearly fully charged.
Two capacitors of 2 μF and 3 μF are connected in series. What is the equivalent capacitance?
Correct Answer: D. 6/5 μF
For series capacitors, 1/Ceq = 1/2 + 1/3 = 5/6 so Ceq = 6/5 μF. Series combination gives a capacitance smaller than the smallest capacitor. In series, the same charge appears on each capacitor.
Two capacitors of 2 μF and 3 μF are connected in parallel. What is the equivalent capacitance?
Correct Answer: A. 5 μF
For parallel capacitors, capacitances add, so Ceq = 2 + 3 = 5 μF. In parallel, each capacitor has the same potential difference across it. Parallel connection increases the ability to store charge at a given voltage.
Which formula gives the energy stored in a capacitor of capacitance C at voltage V?
Correct Answer: D. U = (1/2)CV^2
The energy stored in a capacitor is U = (1/2)CV^2. This energy is stored in the electric field between the plates. It can also be written as U = Q^2/(2C) using Q = CV.