Circuits — Set 3
Physics · परिपथ · Questions 21–30 of 50
A kilowatt-hour (kWh) is a unit of what physical quantity?
Correct Answer: C. Energy
A kilowatt-hour is power multiplied by time, so it represents energy. 1 kWh equals 1000 W used for 3600 s, which is 3600000 J. Electricity bills commonly use kWh as the energy unit.
Why is the metal body of an appliance connected to the earth wire?
Correct Answer: C. To provide a low-resistance path for leakage current
Earthing provides a low-resistance path for any leakage current to flow to ground. This keeps the metal body near zero potential and reduces electric shock risk. A fuse or breaker can then trip quickly when a fault current appears.
What is the main function of a diode in an electric circuit?
Correct Answer: B. It allows current mainly in one direction
A diode conducts mainly in one direction and blocks current in the reverse direction. This property is used for rectification of alternating current. A common diode is made using a semiconductor p-n junction.
In a series circuit containing several resistors, what is true about the current?
Correct Answer: C. It is the same through all resistors
In a series circuit, the same current flows through every component. There is only one path for charge flow in series connection. The total resistance in series is the sum of individual resistances.
In a parallel circuit, what is true about the potential difference across each branch?
Correct Answer: B. It is the same across each branch
In a parallel circuit, each branch is connected across the same two nodes, so voltage is the same. Currents in branches can differ depending on their resistances. Parallel circuits are used in homes so devices get the same supply voltage.
For a cell of emf E and internal resistance r delivering current I, what is the terminal voltage V?
Correct Answer: C. V = E - Ir
When a cell delivers current, the terminal voltage is V = E - Ir due to internal drop. The internal resistance causes a loss of potential inside the cell. When I is zero, terminal voltage equals the emf.
For maximum power transfer from a cell to an external resistor, what should be the relation between load resistance R and internal resistance r?
Correct Answer: B. R = r
Maximum power transfer occurs when the load resistance equals the internal resistance, so R = r. At this condition, the efficiency is not maximum but power delivered to the load is maximum. This idea is used in matching circuits in electronics.
A meter bridge used to find an unknown resistance mainly works on which principle?
Correct Answer: C. Wheatstone bridge principle
A meter bridge is a practical form of the Wheatstone bridge, so it works on the Wheatstone principle. At balance, the galvanometer shows null deflection and ratios of lengths give resistance ratio. Null methods are accurate because they do not depend on galvanometer calibration.
Two equal resistors each of resistance R are connected in parallel. What is the equivalent resistance?
Correct Answer: B. R/2
For two equal resistors in parallel, 1/Req = 1/R + 1/R = 2/R so Req = R/2. Parallel combination provides more paths, reducing overall resistance. If identical resistors are in series, the equivalent becomes 2R instead.
For an ideal ammeter, what is the potential difference across it during measurement?
Correct Answer: B. It is nearly zero
An ideal ammeter has negligible resistance, so the voltage drop across it is nearly zero. This ensures it does not disturb the circuit current significantly. In practice, a small but nonzero resistance causes a tiny drop called burden voltage.