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)

26 NEET-UG practice questions on Experimental Skills (practical physics), part of Physics. The first 25 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
Question 10 · Medium
In an optical-bench experiment with a convex lens, an object pin placed 30 cm from the lens gives a sharp real image 60 cm from the lens on the other side. What is the focal length of the lens?
1. A45 cm
2. B-60 cm
3. C90 cm
4. D20 cm
Answer and explanation in LearnFree account
Question 11 · Hard
To find the resistivity ρ = πd²R/(4L) of a wire, its diameter is read as 0.50 mm on a screw gauge of least count 0.01 mm, its length as 50.0 cm on a metre scale of least count 0.1 cm, and its resistance with an error of 1%. What is the maximum percentage error in ρ?
1. A3.2%
2. B5.2%
3. C4.2%
4. D2.2%
Answer and explanation in LearnFree account
Question 12 · Medium
With its jaws closed, a vernier calliper of least count 0.01 cm shows a zero error of -0.03 cm. Measuring a rod, the main-scale reading is 2.3 cm and the 6th vernier division coincides with a main-scale mark. What is the correct length of the rod?
1. A2.39 cm
2. B2.33 cm
3. C2.36 cm
4. D2.30 cm
Answer and explanation in LearnFree account
Question 13 · Easy
A screw gauge has a pitch of 0.5 mm, and its circular scale has 50 divisions. What is its least count?
1. A0.1 mm
2. B0.025 mm
3. C0.01 mm
4. D0.001 mm
Answer and explanation in LearnFree account
Question 14 · Easy
In the simple pendulum experiment, the length used in T = 2π√(l/g) must be the effective length. What is this length?
1. AFrom the point of suspension to the top of the bob
2. BFrom the point of suspension to the bottom of the bob
3. CFrom the point of suspension to the centre of the bob
4. DThe length of the thread alone, from clamp to hook
Answer and explanation in LearnFree account
Question 15 · Medium
A closed air column first resonates loudly above a vibrating tuning fork of frequency 500 Hz when its measured length is 17 cm. Allowing an end correction of 1 cm, what value does this single reading give for the speed of sound?
1. A320 m/s
2. B340 m/s
3. C180 m/s
4. D360 m/s
Answer and explanation in LearnFree account
Question 16 · Hard
A student cannot measure the radius of a pendulum bob, so she measures only the thread length. The period is 1.2 s for one thread length, and 1.8 s after the thread is lengthened by 45 cm. Taking π² = 10, what value of g does this give?
1. A3.8 m/s²
2. B10 m/s²
3. C5.6 m/s²
4. D50 m/s²
Answer and explanation in LearnFree account
Question 17 · Medium
Match List-I with List-II. List-I (instrument) A. Vernier callipers in which 10 vernier divisions equal 9 main-scale divisions of 1 mm B. Screw gauge of pitch 0.5 mm with 50 circular-scale divisions C. Screw gauge of pitch 1 mm with 50 circular-scale divisions D. Vernier callipers in which 20 vernier divisions equal 19 main-scale divisions of 1 mm List-II (least count) I. 0.02 mm II. 0.1 mm III. 0.05 mm IV. 0.01 mm Choose the correct answer.
1. AA-II, B-IV, C-I, D-III
2. BA-III, B-IV, C-I, D-II
3. CA-II, B-I, C-IV, D-III
4. DA-IV, B-II, C-I, D-III
Answer and explanation in LearnFree account
Question 18 · Medium
In a vernier calliper, 10 vernier divisions coincide with 9 main-scale divisions of 1 mm each. With the jaws closed, the vernier zero lies to the right of the main-scale zero and the 4th vernier division coincides with a main-scale line. A cylinder held between the jaws gives a main-scale reading of 2.3 cm with the 6th vernier division coinciding. What is the corrected diameter of the cylinder?
1. A2.36 cm
2. B2.32 cm
3. C2.40 cm
4. D2.30 cm
Answer and explanation in LearnFree account
Question 19 · Medium
Eight identical small raindrops, each falling through air with terminal velocity v, merge into one larger drop. Assuming Stokes' law applies, what is the terminal velocity of the large drop?
1. Av
2. B4v
3. C8v
4. D2v
Answer and explanation in LearnFree account
Question 20 · Medium
In a simple pendulum experiment the thread is 99.0 cm long from the point of suspension to the top of the bob, and the bob is a sphere of diameter 2.0 cm. Taking g = π² m/s², what is the period for small oscillations?
1. A1.99 s
2. B2.01 s
3. C2.00 s
4. D1.00 s
Answer and explanation in LearnFree account
Question 21 · Medium
A screw gauge has a pitch of 0.5 mm and 50 divisions on its circular scale, and it has a negative zero error of 3 circular-scale divisions. Measuring a wire, the main scale reads 2.5 mm and the circular scale reads 20 divisions. What is the true diameter of the wire?
1. A2.70 mm
2. B2.523 mm
3. C2.73 mm
4. D2.67 mm
Answer and explanation in LearnFree account
Question 22 · Easy
The wire of a meter bridge is usually made of an alloy such as constantan or manganin. What is the main reason?
1. AIt has a very low resistivity, like copper
2. BIt becomes superconducting at room temperature
3. CIts resistance rises sharply with temperature, which increases sensitivity
4. DIts resistance changes very little with temperature
Answer and explanation in LearnFree account
Question 23 · Easy
A student must measure the inner diameter of a narrow glass beaker to a tenth of a millimetre. Which instrument, used in which way, is suitable?
1. AVernier callipers, using its depth rod
2. BVernier callipers, using its inside-measuring jaws
3. CScrew gauge, placing the beaker between its studs
4. DMetre scale, laid across the mouth of the beaker
Answer and explanation in LearnFree account
Question 24 · Hard
In a meter bridge, an unknown resistance X is in the left gap and a 6 Ω resistor in the right gap, and the balance point is 40 cm from the left end. A 3 Ω resistor is now connected in parallel with the 6 Ω resistor. Where is the new balance point, measured from the left end?
1. A40.0 cm
2. B33.3 cm
3. C66.7 cm
4. D30.8 cm
Answer and explanation in LearnFree account
Question 25 · Hard
In an experiment to find Young's modulus, Y = 4MgL/(πd²l), where M is the load, L the wire length, d its diameter and l its extension. The diameter is measured as 0.40 mm and the extension as 0.80 mm, each with an uncertainty of 0.01 mm; M, g and L are taken as exact. What is the maximum percentage error in Y?
1. A3.75%
2. B7.5%
3. C6.25%
4. D5.0%
Answer and explanation in LearnFree account

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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.

In an optical-bench experiment with a convex lens, an object pin placed 30 cm from the lens gives a sharp real image 60 cm from the lens on the other side. What is the focal length of the lens?

To find the resistivity ρ = πd²R/(4L) of a wire, its diameter is read as 0.50 mm on a screw gauge of least count 0.01 mm, its length as 50.0 cm on a metre scale of least count 0.1 cm, and its resistance with an error of 1%. What is the maximum percentage error in ρ?

With its jaws closed, a vernier calliper of least count 0.01 cm shows a zero error of -0.03 cm. Measuring a rod, the main-scale reading is 2.3 cm and the 6th vernier division coincides with a main-scale mark. What is the correct length of the rod?

A screw gauge has a pitch of 0.5 mm, and its circular scale has 50 divisions. What is its least count?

In the simple pendulum experiment, the length used in T = 2π√(l/g) must be the effective length. What is this length?

A closed air column first resonates loudly above a vibrating tuning fork of frequency 500 Hz when its measured length is 17 cm. Allowing an end correction of 1 cm, what value does this single reading give for the speed of sound?

A student cannot measure the radius of a pendulum bob, so she measures only the thread length. The period is 1.2 s for one thread length, and 1.8 s after the thread is lengthened by 45 cm. Taking π² = 10, what value of g does this give?

Eight identical small raindrops, each falling through air with terminal velocity v, merge into one larger drop. Assuming Stokes' law applies, what is the terminal velocity of the large drop?

In a simple pendulum experiment the thread is 99.0 cm long from the point of suspension to the top of the bob, and the bob is a sphere of diameter 2.0 cm. Taking g = π² m/s², what is the period for small oscillations?

A screw gauge has a pitch of 0.5 mm and 50 divisions on its circular scale, and it has a negative zero error of 3 circular-scale divisions. Measuring a wire, the main scale reads 2.5 mm and the circular scale reads 20 divisions. What is the true diameter of the wire?

The wire of a meter bridge is usually made of an alloy such as constantan or manganin. What is the main reason?

A student must measure the inner diameter of a narrow glass beaker to a tenth of a millimetre. Which instrument, used in which way, is suitable?

In a meter bridge, an unknown resistance X is in the left gap and a 6 Ω resistor in the right gap, and the balance point is 40 cm from the left end. A 3 Ω resistor is now connected in parallel with the 6 Ω resistor. Where is the new balance point, measured from the left end?