Assertion (A): As temperature of an electrolyte is increased, its conductivity increases.
Reason (R): Increase of temperature makes the electrolyte less viscous.
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
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Assertion (A) is true. For electrolytes, increased temperature leads to more ion dissociation and reduced viscosity. Reason (R) is true as increased temperature reduces viscosity. (R) correctly explains (A) as lower viscosity allows ions to move more freely, increasing conductivity.
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
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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): The resistivity of a semiconductor decreases with increase in temperature.
Reason (R): In a conductor, the rate of collisions between free electrons and ions increases with increase of 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
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Assertion (A) is true. Increased temperature in semiconductors generates more charge carriers, decreasing resistivity. Reason (R) is also true, as thermal vibrations increase electron-ion collisions in conductors, increasing resistivity. However, (R) explains conductors, not semiconductors, so it's not the correct explanation for (A).
Assertion (A): Terminal potential difference of a cell is always less than its emf.
Reason (R): Potential drop across internal resistance of cell increases terminal potential difference.
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
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Assertion (A) is false. The terminal potential difference \( V \) is equal to emf \( E \) when no current is drawn (open circuit) and can be greater than \( E \) during charging. Reason (R) is false. The potential drop across internal resistance (\( Ir \)) actually decreases the terminal potential difference (\( V = E - Ir \) for discharging).
Assertion (A): A larger dry cell has higher emf.
Reason (R): The emf of a dry cell is proportional to its size.
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
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The electromotive force (EMF) of a cell depends only on the nature of the electrodes and electrolyte, not its size. Size affects internal resistance and current capacity. Both assertion and reason are incorrect.
Assertion (A): A car battery is of \(12\text{ V}\). Eight dry cells of \(1.5\text{ V}\) connected in series can give \(12\text{ V}\). Still such cells are not used in starting a car.
Reason (R): It is easier to start a car engine on a warm day than on a rainy day.
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
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Assertion (A) is true: \(8 times 1.5\text{ V} = 12\text{ V}\). Dry cells have high internal resistance and cannot provide the high current needed to start a car. Reason (R) is also true, as engine oil is less viscous on a warm day. However, (R) does not explain (A).
Assertion (A): When identical cells are connected in parallel to the external load, the effective emf increases.
Reason (R): All the cells will be sending unequal current to the external load in the same direction.
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
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When identical cells are connected in parallel, the effective EMF remains the same as that of a single cell, while the current capacity increases. Thus, Assertion (A) is false. For identical cells, current distribution should be equal. Thus, Reason (R) is also false.
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
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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.
Assertion (A): If an observer is moving with drift speed of electrons in direction opposite to current, observer will not experience any magnetic field.
Reason (R): In the frame of observer charged particles in conductor are at rest.
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
If an observer moves with the electron drift speed (in the direction of electron flow), electrons are at rest relative to them. However, the positive lattice ions, which were stationary in the conductor's frame, are now moving. This motion of positive ions constitutes a current and produces a magnetic field.
Thus, (A) is false. Also, in this frame, only electrons are at rest, while positive ions are moving, so (R) is false.