Question

The following table gives the current $i$ through two devices for several values of potential difference V of Device 1 Device 2 (SI Units).

Device 1	Device 1	Device 2	Device 2
$V$	$I$	$V$	$I$
2	4.5	2	1.5
3	6.75	3	2.2
4	9	4	2.8

• A. Device 1 is ohmic, device 2 is non ohmic.
• B. Device 1 is non ohmic, device 2 is ohmic.
• C. Both are non ohmic.
• D. Both are ohmic.

Answer 1

The correct option is A Device 1 is ohmic, device 2 is non ohmic.

Ohmic Resistance: A resistance can be said to ohmic resistance when the ratio of voltage to instantaneous current is constant.

ie

For ohmic law $R=\frac{V}{I}=constant$

Non-Ohmic Resistance: A resistance can be said to Non-ohmic resistance when the ratio of voltage to instantaneous current is not constant.

ie

For ohmic law $R\ne \frac{V}{I}=constant$

Device 1 Device 2

$\left(1\right)\frac{2}{4.2}=\frac{4}{9}\left(1\right)\frac{2}{1.5}=\frac{4}{3}$

$\left(2\right)\frac{3}{675}=\frac{4}{9}\left(2\right)\frac{3}{2.2}=\frac{15}{11}$

$\left(3\right)\frac{4}{9}=\frac{4}{9}\left(3\right)\frac{4}{2.8}=\frac{10}{7}$

$\because$ The ratio of $\frac{V}{I}$ for device 1 is constant whereas for device 2 is not constant.

$\therefore$ Device 1 is ohmic and Device 2 is non-ohmic.