Potentiometer - comparing emf and internal resistance — practice questions

Question 1 · difficulty L1 · recall

A potentiometer measures emf by a null method, so at balance it draws

• A. maximum current from the test cell
• B. the same current as the primary circuit
• C. no current from the test cell
• D. infinite current

Question 2 · difficulty L1 · understanding

For a uniform potentiometer wire carrying constant current, potential drop along the wire is

• A. proportional to length squared
• B. independent of length
• C. inversely proportional to length
• D. proportional to length

Question 3 · difficulty L2 · understanding

If two cell emfs E1 and E2 balance at lengths l1 and l2 under the same potential gradient,

• A. E1/E2=l1/l2
• B. E1/E2=l2/l1
• C. E1E2=l1/l2
• D. E1-E2=l1+l2

Question 4 · difficulty L2 · application

A cell balances at 80 cm and a reference cell of 1.5 V balances at 60 cm. The unknown emf is

• A. 1.125 V
• B. 2.0 V
• C. 1.5 V
• D. 0.75 V

Question 5 · difficulty L3 · application

For determining a cell's internal resistance, one compares balance lengths for

• A. two unrelated batteries only
• B. the wire resistance at two temperatures only
• C. open-circuit emf and terminal voltage with a known external load
• D. current with the key always open

Question 6 · difficulty L3 · application

If emf E, terminal voltage V and external resistance R are known, cell internal resistance is

• A. r=R(V/E-1)
• B. r=EV/R
• C. r=R+E/V
• D. r=R(E/V-1)

Question 7 · difficulty L4 · analysis

Why is a potentiometer generally more accurate for emf than a voltmeter?

• A. At null it draws essentially no current from the source being measured
• B. It always has zero wire resistance
• C. It amplifies voltage electronically in the basic experiment
• D. It ignores potential gradients

Question 8 · difficulty L4 · analysis

If primary current in the potentiometer wire is increased, the potential gradient k

• A. decreases
• B. increases
• C. remains fixed
• D. becomes zero

Question 9 · difficulty L5 · analysis

If potential gradient becomes too large, the balance length for a given emf becomes

• A. longer
• B. unchanged
• C. shorter
• D. negative

Question 10 · difficulty L5 · analysis

A cell has E=1.5 V and terminal voltage 1.2 V across R=4 Ω. Its internal resistance is

• A. 0.25 Ω
• B. 5 Ω
• C. 4 Ω
• D. 1 Ω