Resistivity using a metre bridge — NEET & JEE 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 L2 · understanding

At balance in a metre bridge, the result follows from the Wheatstone-bridge condition because

• A. no current flows through the galvanometer
• B. the battery current is zero
• C. both gap resistances must be equal
• D. the wire has zero resistance

Question 6 · 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 7 · 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 8 · difficulty L3 · application

An unknown resistance X is in the left gap and a 3 ohm standard resistance is in the right gap of a metre bridge. Balance occurs at 40 cm from the left end. What is X?

• A. 2 ohm
• B. 3 ohm
• C. 4.5 ohm
• D. 7.5 ohm

Question 9 · difficulty L3 · application

A wire has resistance 2.0 ohm, length 1.0 m and cross-sectional area $5.0\times10^{-7}$ m$^2$. Its resistivity is

• A. $1.0\times10^{-6}$ ohm m
• B. $4.0\times10^{6}$ ohm m
• C. $2.5\times10^{-7}$ ohm m
• D. $1.0\times10^{-7}$ ohm m

Question 10 · 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