Assertion (A): In a Meter Bridge experiment, null point for an unknown resistance is measured. Now, the unknown resistance is put inside an enclosure maintained at a higher temperature. The null point can be obtained at the same point as before by decreasing the value of the standard resistance.
Reason (R): Resistance of a metal decreases with increase in temperature.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is false. If the unknown resistance (presumably metallic) is heated, its resistance increases. To maintain the null point at the same position in a Meter Bridge (\(R_{\text{unknown}} / R_{\text{standard}} = L_1 / L_2\)), the standard resistance must also be *increased* proportionally, not decreased. Reason (R) is false. For metals, resistance generally *increases* with an increase in temperature, not decreases.
Assertion (A): In the given circuit, when switch \(S\) is ON reading of ammeter and voltmeter will increase.
Reason (R): In parallel combination net resistance will reduce.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer
When switch \(S\) is ON, another resistor \(R\) is connected in parallel. The equivalent resistance of the parallel combination is \(R/2\), which is less than \(R\). Thus, the net resistance reduces (Reason R is true). The total current (ammeter reading) will increase. However, assuming an ideal voltage source, the voltage across the parallel combination (voltmeter reading) will remain constant (equal to the source EMF). Therefore, Assertion (A) is false as the voltmeter reading does not increase.
Assertion (A): Resistance of ammeter is less than resistance of milliammeter, (If made from same galvanometer).
Reason (R): Value of shunt resistance in case of ammeter is more than a milliammeter.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer
An ammeter is designed to measure larger currents than a milliammeter. To achieve a larger current range with the same galvanometer, a smaller shunt resistance is required to bypass a greater portion of the total current. A smaller shunt resistance results in a lower overall resistance for the ammeter. Thus, Assertion (A) is true. Reason (R) states the shunt resistance for an ammeter is more than a milliammeter, which is false; it must be less.
Assertion (A): A voltmeter is an inherently inaccurate instrument.
Reason (R): A voltmeter is always connected in parallel in a circuit.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer
Assertion (A) is true, as any real voltmeter has finite resistance and draws some current, perturbing the circuit. Reason (R) is true; voltmeters are always connected in parallel. However, (R) is not the correct explanation for (A).
Assertion (A): Thick metallic strips are used to join wires in a potentiometer.
Reason (R): Metallic strips are used to provide mechanical support to potentiometer wires.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer
Potentiometers use thick metallic strips to minimize their resistance, ensuring negligible potential drop across them compared to the main potentiometer wire. Reason (R) is incorrect; mechanical support is a secondary benefit, not the primary reason. Thus, A is true and R is false.
Assertion (A): The emf of the driver cell in the potentiometer experiment should be greater than the e.m.f. of the cell to be determined.
Reason (R): The fall of potential drop across the potentiometer wire should be less than the e.m.f. of the cell to be determined.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer
For a potentiometer to function, the driver cell's EMF must exceed the unknown EMF to ensure a balancing point can be found. The potential drop across the entire potentiometer wire must be greater than the unknown EMF. Reason (R) states the opposite, making it false.
Assertion (A): A potentiometer of longer length is used for accurate measurement.
Reason (R): The potential gradient for a potentiometer of longer length with a given source of e.m.f. becomes small.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer
A longer potentiometer wire, for a given driver cell, results in a smaller potential gradient \( k = V/L \). A smaller potential gradient means that even a small change in potential corresponds to a significant change in balancing length, increasing the sensitivity and accuracy of the measurement. Thus, both (A) and (R) are true, and (R) correctly explains (A).
Assertion (A): A galvanometer can be used as an ammeter only.
Reason (R): A galvanometer can be used in electric circuit to detect the electric current only.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer
A galvanometer is a device used to detect small electric currents. It can be converted into an ammeter by connecting a low resistance shunt in parallel or into a voltmeter by connecting a high resistance in series. Therefore, the assertion that it can be used 'only' as an ammeter is false, and the reason that it can be used to detect current 'only' is also false. Thus, both A and R are false.
Assertion (A): Electric appliances with a metallic body have three pin connections whereas an electric bulb has two pin connections.
Reason (R): Three pin connection reduces heating of connecting cable.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is true. Metallic-bodied appliances require a third pin for earthing for safety. Electric bulbs usually do not. Reason (R) is false. The third pin (earth) is for safety, to prevent electric shock in case of a fault, not to reduce cable heating.
Assertion (A): In a balanced Wheatstone bridge, the current through cell depends on resistance of galvanometer.
Reason (R): At balanced condition current through galvanometer is non-zero.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
In a balanced Wheatstone bridge, the current through the galvanometer is zero. Hence, the galvanometer's resistance does not affect the equivalent resistance of the bridge and thus the current drawn from the cell. Both Assertion (A) and Reason (R) are false.