Ohm's law and figure of merit of a galvanometer — practice questions

Question 1 · difficulty L1 · recall

Ohm's law for an ohmic conductor at constant temperature is

• A. V=IR
• B. V=I/R
• C. V=R/I
• D. VI=R

Question 2 · difficulty L1 · understanding

A V-I graph for an ohmic resistor is

• A. a circle
• B. a straight line through the origin
• C. always horizontal
• D. an exponential decay

Question 3 · difficulty L2 · understanding

If a V-versus-I graph has slope 5 V/A, resistance is

• A. 0.2 Ω
• B. 25 Ω
• C. 5 Ω
• D. 5 A

Question 4 · difficulty L2 · application

The figure of merit k of a galvanometer is commonly defined as

• A. deflection per unit voltage only
• B. resistance per unit current
• C. voltage required per metre
• D. current required per unit scale division of deflection

Question 5 · difficulty L3 · application

If a galvanometer current of 20 μA produces 40 divisions, its figure of merit is

• A. 0.5 μA/division
• B. 2 μA/division
• C. 800 μA/division
• D. 20 μA/division

Question 6 · difficulty L3 · application

Why should resistor temperature be kept nearly constant when verifying Ohm's law?

• A. Voltage has no meaning at different temperature
• B. Resistance can change with temperature
• C. Current ceases to flow if warm
• D. Ohm's law requires zero resistance

Question 7 · difficulty L4 · analysis

A resistor carries 0.20 A at 3.0 V and 0.40 A at 6.0 V. These readings are consistent with resistance

• A. 7.5 Ω
• B. 30 Ω
• C. 15 Ω
• D. 1.5 Ω

Question 8 · difficulty L4 · analysis

For a galvanometer experiment using a known series resistance, increasing series resistance at fixed source voltage tends to

• A. increase current without limit
• B. leave current exactly unchanged
• C. reverse current automatically
• D. reduce galvanometer current and deflection

Question 9 · difficulty L5 · analysis

If the measured current scale calibration has a zero offset, best practice is to

• A. apply the appropriate zero correction before calculating the figure of merit
• B. ignore it because ratios cancel always
• C. double every current
• D. change the galvanometer resistance by hand

Question 10 · difficulty L5 · analysis

A galvanometer has k=2 μA/div. A deflection of 25 divisions corresponds to current

• A. 12.5 μA
• B. 50 μA
• C. 27 μA
• D. 2 μA