Current Electricity Class 12 Physics MCQs Pdf
41. The electron drift speed is estimated to be only a few mm s-1 for currents in the range of a few amperes? How then is current established almost the instant a circuit is closed?
Answer/Explanation
Answer:
Explaination:
It is the electric field which spreads throughout a circuit with speed of light.
At every point, a local electron drift is induced by the field. This way, the
current attains its steady value almost instantaneously.
42. Is there a net field inside the cell when the circuit is closed and a steady current passes through? Explain.
Answer/Explanation
Answer:
Explaination:
When circuit is closed, the current flows in the direction of electrostatic
field outside, and opposite to the direction of electrostatic field inside the
cell. The latter fact shows that there is a net field inside the cell opposite
to the electrostatic field.
43. Plot a graph showing the variation of resistance of a conducting wire as a function of its radius, keeping the length of the wire and its temperature as constant. [Foreign 2013]
Answer/Explanation
Answer:
Explaination:
44. V-I graph for a metallic wire at two different temperatures Tx and T2 is as shown
in the figure. Which of the two temperatures is higher and why?
Answer/Explanation
Answer:
Explaination:
Since, resistance = slope of V – I graph. In the figure, the slope of Tx
is large, so T1 represents the higher temperature as the resistance
increases with the temperature for a conductor.
45. The emf of a cell is always greater than its terminal voltage. Why? Give reason. [Delhi 2013]
Answer/Explanation
Answer:
Explaination:
The current always flows from higher to lower potential. To produce the current
to an external circuit, the emf must be greater than the terminal voltage, i.e.
the potential difference across the external circuit.
ε = V + Ir
46. You are given three constantan wires P, Q and R of length and area of cross-section (L, A), (2L, \(\frac{A}{2}\)), (\(\frac{L}{2}\)2A) respectively. Which has highest resistance? [DoE]
Answer/Explanation
Answer:
Explaination:
47. Two wires of equal length, one of copper and the other of manganin have the same resistance. Which wire is thicker? [AI2012]
Answer/Explanation
Answer:
Explaination:
As the resistivity of manganin (2) is greater than the resistivity of
copper (1). So, the manganin wire is thicker.
48. Nichrome and copper wires of same length and same radius are connected in series. Current/is passed through them. Which wire gets heated up more? Justify your answer. [AI 2017]
Answer/Explanation
Answer:
Explaination:
Nichrome wire having more resistivity () will heat up more, as heat produced =
I²R = I²\(\frac{l}{A}\)
49. State the condition for maximum current to be drawn from a cell.
Answer/Explanation
Answer:
Explaination:
\(I=\frac{E}{R+r}\); when the external resistance,
R = 0 (i.e. cell is short-circuited), then the maximum current will be drawn
from a cell.
50. State the condition under which the terminal potential difference across a battery and its emf are equal.
Answer/Explanation
Answer:
Explaination:
∵ V = E – Ir, when the battery is in open circuit, i.e. no current is
being drawn from the cell. Therefore, terminal potential difference is equal to
the emf to the cell.