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#	Question	Answer
1	What is the SI unit of electric current?	Ampere (A).
2	Is there a net current in a conductor in the absence of an electric field?	No.
3	What is resistivity?	A material property that determines the resistance of a conductor of given dimensions.
4	What is relaxation time?	The average time between successive collisions of electrons with ions.
5	What is the formula for mobility?	\( \mu = \frac{e\tau}{m} \).
6	Why do electrons acquire a steady drift speed?	Because acceleration is interrupted by collisions with ions, resulting in a constant average velocity.
7	What is the temperature coefficient of resistivity?	The fractional change in resistivity per unit change in temperature.
8	A nichrome heating element has a resistance of 75.3 Ω at 27°C. When connected to 230 V, the current is 2.68 A. What is the steady temperature of the element? (\( \alpha = 1.70 \times 10^{-4} \, {}^\circ\text{C}^{-1} \))	847°C.
9	What is the terminal voltage of a cell when a current \( I \) is flowing?	\( V = \varepsilon - Ir \).
10	What is the maximum current that can be drawn from a cell?	\( I_{max} = \frac{\varepsilon}{r} \).
11	What is the equivalent internal resistance of two cells connected in parallel?	\( r_{eq} = \frac{r_1 r_2}{r_1 + r_2} \).
12	Why is Kirchhoff's junction rule true?	Because charge is conserved (no accumulation of charge at a junction in steady state).
13	What is a Wheatstone bridge used for?	To measure an unknown resistance.
14	In the network of Example 3.6, what is the current in branch AB?	\( \frac{5}{8} \) A.
15	What is the formula for resistivity in terms of electron parameters?	\( \rho = \frac{m}{ne^2 \tau} \).
16	A car battery has an emf of 12 V and internal resistance of 0.4 Ω. What is the maximum current that can be drawn?	30 A.
17	A nichrome heating element connected to 230 V draws an initial current of 3.2 A which settles to 2.8 A. What is the steady temperature? (\( \alpha = 1.70 \times 10^{-4} \, {}^\circ\text{C}^{-1} \), room temperature 27°C)	867°C.
18	How is the SI unit ampere actually defined?	Through the magnetic effects of currents (covered in the next chapter), not directly from the current formula itself.
19	What analogy led Ohm to his law?	An analogy with heat conduction: electric field is analogous to the temperature gradient, and electric current is analogous to heat flow.
20	What kind of V-I behaviour does GaAs exhibit that violates Ohm's law?	The relation between V and I is not unique — there is more than one value of V for the same current I (it shows a negative-resistance region).
21	Why are materials like nichrome, manganin, and constantan used in wire-bound standard resistors?	Their resistivity has a very weak dependence on temperature, so their resistance values change very little with temperature.
22	When can the internal resistance of a cell be neglected in practical calculations?	When the current I is such that \( \varepsilon \gg Ir \).
23	Is the equation V = IR itself a statement of Ohm's law?	No — this equation simply defines resistance R and applies to any conducting device, whether it obeys Ohm's law or not. Ohm's law is the additional assertion that R is independent of V (i.e. the I-vs-V plot is linear).
24	A cell of emf 12 V and internal resistance 2 Ω delivers a current of 0.6 A. What is its terminal voltage? (NEET 2026)	10.8 V.
25	Two heaters, rated 1 kW and 2 kW at the same voltage, are first connected in series and then in parallel across that same voltage. What is the ratio of total power dissipated in the series case to the parallel case? (NEET 2024)	2 : 9.
26	A platinum wire has resistance 2 Ω at 0°C and 6.8 Ω at 80°C. What is its temperature coefficient of resistance? (NEET 2023)	\( 3 \times 10^{-2} \) °C⁻¹.
27	Resistors of 100 Ω and 200 Ω are connected in parallel across the same supply. What is the ratio of heat dissipated in the 100 Ω resistor to that in the 200 Ω resistor? (NEET 2022)	2 : 1 — with the same voltage across both, \( P = V^2/R \), so the smaller resistor dissipates more power, in inverse proportion to R.
28	A time-varying charge \( Q = at - bt^2 \) flows through a resistor R, where the current falls to zero at \( t = a/2b \). What is the total heat dissipated in R up to that time? (NEET 2016)	\( \frac{a^3 R}{6b} \) — found by integrating \( I^2R \), with \( I = dQ/dt = a - 2bt \), from \( t=0 \) to \( t=a/2b \).