Question

To study the dependence of current (I) on the potential difference (V) across a resistor, the following observations were made by four students A, B, C and D.

Student	Reading No. 1	Reading No. 2	Reading No. 3
A	V = 0.5 V I = 0.1 A	V = 1.0 V I = 0.2 A	V = 1.5 V I = 0.3 A
B	V = 0.8 V I = 0.4 A	V = 1.6 V I = 0.8 A	V = 2.4 V I = 1.2 A
C	V = 1.0 V I = 0.5 A	V = 1.2 V I = 1.4 A	V = 1.4 V I = 1.0 A
D	V = 2.4 V I = 0.8 A	V = 2.7 V I = 0.9 A	V = 3.0 V I = 1.0 A

The teacher found that one of the students has made wrong observations. The student who made the mistake is:
(1) A
(2) B
(3) C
(4) D

Answer 1

According to Ohm's Law, $V=IR\mathrm{or}\frac{V}{I}=R$ (Where 'R' is the constant and is given by resistance of the circuit)

While observing the current-voltage relationship across a resistor, all of the readings must follow this law. That means Voltage and current ratio should be a constant value in every case.

All of the readings taken by students A, B and D give the same value of the voltage-current ratio, but the observations made by student C don't. All the three readings observed by student C give a different value of the voltage-current ratio (resistance of the circuit), which is not possible. So, student C has made wrong observations.

Hence, the correct answer is option 3.