A student measures the period T of a simple pendulum for several lengths l. Which plot is a straight line, and how is g found from it?

T against √l; g = 4π² × slope

T² against l; g = 4π² × slope

When finding an unknown resistance with a meter bridge, why is the known resistance usually chosen so that the null point lies near the middle of the wire?

It keeps the percentage error in the calculated resistance small

It makes the wire's resistance per unit length uniform

It makes the galvanometer current largest at balance

It removes the need for a known resistance

Experimental Skills (practical physics)

9 NEET-UG practice questions on Experimental Skills (practical physics), part of Physics. The first 9 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
One full turn of a micrometer screw advances it by 1 mm, and its head carries 100 divisions. It reads -0.03 mm with the jaws shut. A ball bearing gives a linear reading of 3 mm and a head reading of 47 divisions. Find the true diameter.
1. A3.44 mm
2. B3.47 mm
3. C3.27 mm
4. D3.50 mm
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Answer: D · 3.50 mm
Least count = 1/100 = 0.01 mm. Observed reading = 3 + 47 × 0.01 = 3.47 mm. Corrected reading = observed - zero error = 3.47 - (-0.03) = 3.50 mm.
- A: The negative sign of the zero error was ignored.
- B: No zero correction was applied.
- C: The least count was taken as 0.005 mm.
Remember this
True reading equals observed reading minus zero error, with the sign of the zero error kept.
Question 2 · Easy
A student measures the period T of a simple pendulum for several lengths l. Which plot is a straight line, and how is g found from it?
1. AT against √l; g = 4π² × slope
2. BT against l; g = 4π²/slope
3. CT² against l; g = 4π² × slope
4. DT² against l; g = 4π²/slope
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Answer: D · T² against l; g = 4π²/slope
From T = 2π√(l/g), T² = (4π²/g) l, so T² against l is a straight line through the origin with slope 4π²/g. Hence g = 4π²/slope.
- A: T against √l is straight but has slope 2π/√g, which does not give this formula.
- B: T against l is a curve, not a straight line.
- C: The slope is 4π²/g, so g is not 4π² times the slope.
Remember this
Squaring T = 2π√(l/g) gives a straight line of slope 4π²/g on a T² against l plot.
Question 3 · Medium
When finding an unknown resistance with a meter bridge, why is the known resistance usually chosen so that the null point lies near the middle of the wire?
1. AIt makes the wire's resistance per unit length uniform
2. BIt makes the galvanometer current largest at balance
3. CIt removes the need for a known resistance
4. DIt keeps the percentage error in the calculated resistance small
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Answer: D · It keeps the percentage error in the calculated resistance small
The unknown is found from X = R l/(100 - l). Near the middle, l and 100 - l are both large, so the same error in reading them, and the end resistance, have the least relative effect.
- A: The wire's uniformity is a property of the wire, not of the null position.
- B: At balance the galvanometer current is zero.
- C: The known resistance is still needed in the formula.
Remember this
A null point near the wire's middle reduces the percentage error, since both balancing lengths are large.
Question 4 · Medium
Steel balls of different radii r are released in a tall jar of glycerine, and their terminal velocities v are recorded. Assuming Stokes' law holds, which plot gives a straight line through the origin?
1. Av against r³
2. Bv against r
3. Cv against r²
4. Dv against 1/r
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Answer: C · v against r²
At terminal velocity the weight less the upthrust balances 6πηrv, which gives v = 2r²(ρ - σ)g/(9η). So v is directly proportional to r², and that plot is a straight line through the origin.
- A: r³ comes from the volume alone; the drag's factor of r has been ignored.
- B: Viscous drag depends on r, but weight on r³, so v goes as r².
- D: v rises with radius, it does not fall.
Remember this
Terminal velocity varies as r² and as (ρ - σ), and inversely as viscosity.
Question 5 · Medium
In a simple pendulum experiment, length is measured with a maximum relative error of 1% and period with a maximum relative error of 2%. What is the maximum relative error in the value of g found from T = 2π√(l/g)?
1. A3%
2. B5%
3. C4%
4. D6%
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Answer: B · 5%
Rearranging, g = 4π²l/T². Maximum relative errors add, with powers as multipliers: Δg/g = Δl/l + 2 ΔT/T = 1% + 4% = 5%.
- A: The power of 2 on T was not applied.
- C: The error in the length was left out.
- D: The factor 2 was applied to the length error too.
Remember this
In a product of powers, each relative error is multiplied by the size of its power, and the results always add.
Question 6 · Easy
On a Vernier callipers, one main scale division is 0.5 mm, and 20 Vernier divisions coincide with 19 main scale divisions. What is the least count?
1. A0.475 mm
2. B0.05 mm
3. C0.025 mm
4. D0.5 mm
Answer and explanation in LearnFree account
Question 7 · Medium
A wire 2 m long with cross-section 1 mm² extends by 0.5 mm when a 5 kg mass hangs from it. Taking g = 10 m/s², what value of Young's modulus does this give?
1. A1 × 10¹¹ Pa
2. B2 × 10⁸ Pa
3. C2 × 10¹¹ Pa
4. D2 × 10¹⁰ Pa
Answer and explanation in LearnFree account
Question 8 · Hard
A meter bridge has X in the left gap and Y in the right gap. The null point is 25 cm from the left end. A 10 Ω resistor is then added in series with X, and the null point moves to 50 cm. What is X?
1. A3.3 Ω
2. B5 Ω
3. C15 Ω
4. D10 Ω
Answer and explanation in LearnFree account
Question 9 · Hard
An air column closed at one end is excited by a fork of frequency 420 Hz. Loud responses are first heard at column lengths of 19.0 cm and 59.0 cm. Find the speed of sound and the end correction.
1. A168 m/s and 1.0 cm
2. B319 m/s and 0 cm
3. C336 m/s and 1.0 cm
4. D336 m/s and 2.0 cm
Answer and explanation in LearnFree account

Experimental Skills (practical physics)

One full turn of a micrometer screw advances it by 1 mm, and its head carries 100 divisions. It reads -0.03 mm with the jaws shut. A ball bearing gives a linear reading of 3 mm and a head reading of 47 divisions. Find the true diameter.

A student measures the period T of a simple pendulum for several lengths l. Which plot is a straight line, and how is g found from it?

When finding an unknown resistance with a meter bridge, why is the known resistance usually chosen so that the null point lies near the middle of the wire?

Steel balls of different radii r are released in a tall jar of glycerine, and their terminal velocities v are recorded. Assuming Stokes' law holds, which plot gives a straight line through the origin?

In a simple pendulum experiment, length is measured with a maximum relative error of 1% and period with a maximum relative error of 2%. What is the maximum relative error in the value of g found from T = 2π√(l/g)?

On a Vernier callipers, one main scale division is 0.5 mm, and 20 Vernier divisions coincide with 19 main scale divisions. What is the least count?

A wire 2 m long with cross-section 1 mm² extends by 0.5 mm when a 5 kg mass hangs from it. Taking g = 10 m/s², what value of Young's modulus does this give?

A meter bridge has X in the left gap and Y in the right gap. The null point is 25 cm from the left end. A 10 Ω resistor is then added in series with X, and the null point moves to 50 cm. What is X?

An air column closed at one end is excited by a fork of frequency 420 Hz. Loud responses are first heard at column lengths of 19.0 cm and 59.0 cm. Find the speed of sound and the end correction.