The current-voltage graph for a given speciment at two different temperatures `T_1` and `T_2` are shown in the figure. Is the specimen ohmic ?
(b) At which temperature resistance is greater ?
( c) Which temperature is higher ?
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Explanation

(a)Since `I-V` graph is linear i.e., `V alpha I`, the specimen is ohmic.
(b) The slope of `I-V` gives reciprocal of resistance.
`R = (V)/(I) = (1)/(tan theta)`
`theta_1 gt theta_2` i.e., `tan theta_1 gt tan theta_2` so `R_1 lt R_2`
At temperature `T_2`, resistance is greater.
( c) `R_2 gt R_1, T_2 gt T_1`
Resistance increases with temperature.