Assertion (A): Though the same current flows through the line wires and the filament of the bulb but the rate of heat produced in the filament is much higher than that in line wires.
Reason (R): The filament of bulbs is made of a material of high resistance and low melting point.
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 because heat produced is \( H = I^2 R t \) and the filament has a much higher resistance \( R \). Reason (R) is false because filaments (like tungsten) have a *high* melting point to withstand high temperatures.
Assertion (A): Electrolyte are more conducting than metal.
Reason (R): Ions moves faster than electrons.
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 false; metals are generally far better conductors than electrolytes. Reason (R) is also false; electrons typically move faster than ions, and metals have a much higher density of charge carriers.
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): Electric field is present in the vicinity of a current carrying wire.
Reason (R): The principle of conservation of charge is not followed, when charges are in motion.
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; an electric field is necessary to drive current through a wire. Reason (R) is false; the principle of conservation of charge is a fundamental law and holds true even when charges are in motion.
Assertion (A): In real battery total chemical energy lost in the battery can not be obtained at load resistance.
Reason (R): Two heaters with different resistance are connected in parallel. Higher resistance heater will glow more.
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 due to the internal resistance of real batteries, which dissipates some chemical energy as heat. Reason (R) is false; for parallel connections, power \( P = V^2 / R \), so the heater with *lower* resistance will glow more.
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): The coil of a heater is cut into two equal halves and only one of them is used into heater. The heater will now require half the time to produce the same amount of heat.
Reason (R): The heat produced is directly proportional to the square of current.
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 the heater coil is cut in half, its resistance becomes \( R' = R/2 \). Since \( H = \frac{V^2}{R}t \), for the same heat \( H \) and constant voltage \( V \), the time \( t \) is proportional to \( R \). Halving \( R \) halves \( t \). So (A) is true. (R) is also true by Joule's law, but it does not explain (A) because (A) implicitly assumes constant voltage, where \( I \) would change.
Assertion (A): The bending of an insulated wire increases the resistance of wire.
Reason (R): The drift velocity of electrons in bent wire decreases.
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
Resistance of a wire \( R = \rho \frac{L}{A} \) primarily depends on its resistivity \( rho \), length \( L \), and cross-sectional area \( A \). Bending an insulated wire does not significantly alter these properties, so its resistance does not increase. Drift velocity is not affected by bending either. Therefore, both (A) and (R) are 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).