Circuits — Set 5
Physics · परिपथ · Questions 41–50 of 50
If a resistor has resistance R, what is its conductance G?
Correct Answer: D. G = 1/R
Conductance is defined as the reciprocal of resistance, so G = 1/R. It measures how easily current can flow for a given voltage. Its unit is siemens, which equals ampere per volt.
The emf of a source is best defined as what quantity?
Correct Answer: B. Work done by the source per unit charge
Emf is the work done by the source per unit charge to drive charge around the circuit. Its unit is volt, the same as potential difference. Emf is a property of the source and is not the same as terminal voltage under load.
When a cell is not supplying any current, what is its terminal voltage approximately equal to?
Correct Answer: A. Its emf
When no current flows, there is no internal drop, so terminal voltage equals the emf. This is called the open-circuit voltage. When the cell delivers current, terminal voltage becomes less than emf for a real cell.
In a balanced Wheatstone bridge with resistances P, Q, R, and S, which relation holds?
Correct Answer: D. P/Q = R/S
At balance in a Wheatstone bridge, the ratio P/Q equals R/S. This balance gives zero current through the galvanometer branch. The bridge is widely used to compare resistances without drawing galvanometer current.
A fuse wire is generally made of an alloy with which property?
Correct Answer: B. Low melting point
A fuse wire is made from an alloy with a low melting point so it melts quickly on overcurrent. Melting breaks the circuit and prevents overheating damage. Common fuse alloys include combinations of tin and lead.
What is the main purpose of a fuse in an electrical circuit?
Correct Answer: B. To protect the circuit by breaking it during excessive current
A fuse protects a circuit by melting and breaking the circuit when current becomes excessive. This prevents wires and devices from overheating and catching fire. A fuse is always connected in series with the live line of the circuit.
In steady direct current conditions, an ideal capacitor behaves like what?
Correct Answer: A. An open circuit
In steady DC, an ideal capacitor becomes fully charged and then no current flows, so it acts as an open circuit. Current flows only during charging or discharging when voltage is changing. Capacitors are used to block DC while allowing changing signals to pass.
What is the time constant τ of an RC circuit?
Correct Answer: D. τ = RC
The time constant of an RC circuit is τ = RC. It sets the characteristic time for exponential charging or discharging. Larger R or larger C makes the response slower.
When capacitors are connected in series, what is the same for each capacitor?
Correct Answer: B. Charge on each is the same
In series, the same charge flows through the path, so each capacitor carries the same charge. The voltages across capacitors can be different depending on capacitances. Series capacitors are used to achieve a smaller equivalent capacitance and higher voltage rating.
In a parallel combination of resistors, which statement is always true about equivalent resistance?
Correct Answer: D. It is less than the smallest branch resistance
In parallel, current has multiple paths, so the equivalent resistance is less than the smallest branch resistance. This follows from 1/Req being the sum of positive terms 1/Ri. Adding more parallel branches makes Req decrease further.