Q4. Assertion: in this experiment the V–I graph of the wire is a straight line through the origin. Reason: the wire obeys Ohm’s law, V = RI, with R constant while the temperature stays the same. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion (NCERT Eq. (3.3), page 83; temperature, NCERT Section 3.8, page 90).
Q5. Two points on the best straight line of a V–I graph are (0.15 A, 0.90 V) and (0.45 A, 2.70 V). Find the resistance.
Slope = (2.70 − 0.90)/(0.45 − 0.15) = 1.80/0.30 = 6.0 Ω (NCERT Eq. (3.3), page 83).
Q6. A student plots I against V and finds a slope of 0.25 A V−1. What is the resistance?
On an I–V graph the slope is 1/R, so R = 1/0.25 = 4.0 Ω (from NCERT Eq. (3.3), page 83).