Assertion (A): A car engine can be started more easily on a warm day than on a cold day.
Reason (R): EMF of battery is more on a cold day.
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
It is a common observation that starting a car engine is more difficult on a cold day due to several factors including increased viscosity of engine oil and reduced battery performance. So, Assertion (A) is true. On a cold day, the chemical reactions inside a battery slow down, leading to an increase in its internal resistance and a decrease in its effective capacity, rather than an increase in EMF. The EMF generally tends to slightly decrease or remain similar. So, Reason (R) is false.
Assertion (A): The electric bulb glows immediately when switch is on.
Reason (R): The drift velocity of electrons in a metallic wire is very high (near speed of light).
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 the electric field propagates very quickly, causing electrons to move almost instantly. Reason (R) is false; the drift velocity of electrons is very slow, typically \( 10^{-4} \text{ m/s} \) to \( 10^{-5} \text{ m/s} \).
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
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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.