Resistivity using a metre bridge — practice questions

Question 1 · difficulty L1 · recall

A metre bridge works on the principle of

• A. Faraday induction
• B. photoelectric emission
• C. Wheatstone bridge balance
• D. total internal reflection

Question 2 · difficulty L1 · understanding

At balance in an ideal metre bridge, the galvanometer current is

• A. maximum
• B. equal to battery current
• C. independent of slider position
• D. zero

Question 3 · difficulty L2 · understanding

If unknown resistance X is in one gap and known R in the other, balance length l from the X side gives approximately

• A. X/R = l/(100-l)
• B. X/R=(100-l)/l always regardless of placement
• C. X+R=l
• D. XR=100l

Question 4 · difficulty L2 · application

Resistivity of a wire is related to resistance by

• A. ρ=RL/A
• B. ρ=RA/L
• C. ρ=L/(RA)
• D. ρ=R/L only

Question 5 · difficulty L3 · application

A balance point very close to 0 or 100 cm is undesirable mainly because

• A. the bridge law becomes mathematically false
• B. current becomes exactly zero everywhere
• C. fractional uncertainty and end effects become larger
• D. resistance of the wire vanishes

Question 6 · difficulty L3 · application

Interchanging the known and unknown resistances and repeating the measurement helps to

• A. double the unknown resistance physically
• B. eliminate the need for a null point
• C. change resistivity with direction
• D. reduce certain systematic end errors

Question 7 · difficulty L4 · analysis

A bridge balances at 40 cm with unknown X in the left gap and R=6 Ω in the right. X is

• A. 4 Ω
• B. 9 Ω
• C. 6 Ω
• D. 2.4 Ω

Question 8 · difficulty L4 · analysis

If a specimen wire's measured diameter is too large, calculated resistivity ρ=Rπd²/(4L) will be

• A. too small
• B. too large
• C. unchanged
• D. negative

Question 9 · difficulty L5 · analysis

Why should the bridge key be closed only while taking readings in many school experiments?

• A. To increase wire temperature intentionally
• B. To eliminate current from the circuit
• C. To limit heating that could change resistance
• D. To make the scale longer

Question 10 · difficulty L5 · analysis

An unknown resistance is close to the known resistance. The most sensitive balance point is expected near

• A. 0 cm
• B. 100 cm
• C. either extreme only
• D. 50 cm