# Young’s Modulus Questions and Answers ### Young’s Modulus and Breaking Stress:

Ques: The Poisson’s ratio cannot have the value
(a) 0.7
(b) 0.2
(c) 0.1
(d) 0.5

Ans. (a)

Ques: The length of an iron wire is L and area of cross-section is A. The increase in length is l on applying the force F on its two ends. Which of the statement is correct
(a) Increase in length is inversely proportional to its length L
(b) Increase in length is proportional to area of cross-section A
(c) Increase in length is inversely proportional to A
(d) Increase in length is proportional to Young’s modulus

Ans. (c)

Ques: In the Young’s experiment, If length of wire and radius both are doubled then the value of Y will become
(a) 2 times
(b) 4 times
(c) Remains same
(d) Half

Ans. (c)

Ques: The breaking stress of a wire depends upon
(a) Length of the wire
(c)

Material of the wire
(d) Shape of the cross section

Ans. (c)

Ques: A pan with set of weights is attached with a light spring. When disturbed, the mass-spring system oscillates with a time period of 0.6 s. When some additional weights are added then time period is 0.7s. The extension caused by the additional weights is approximately given by
(a) 1.38 cm
(b) 3.5 cm
(c) 1.75 cm
(d) 2.45 cm

Ans. (b)

Ques: The ratio of the lengths of two wires A and B of same material is 1 : 2 and the ratio of their diameter is 2 : 1. They are stretched by the same force, then the ratio of increase in length will be
(a) 2 : 1
(b) 1 : 4
(c) 1 : 8
(d) 8 : 1

Ans. (c)

Ques: A wire of length 2 m is made from 10 cm3 of copper. A force F is applied so that its length increases by 2 mm. Another wire of length 8 m is made from the same volume of copper. If the force F is applied to it, its length will increase by
(a) 0.8 cm
(b) 1.6 cm
(c) 2.4 cm
(d) 3.2 cm

Ans. (d)

Ques: The dimensions of four wires of the same material are given below. In which wire the increase in length will be maximum when the same tension is applied
(a) Length 100 cm, Diameter 1 mm
(b) Length 200 cm, Diameter 2 mm
(c) Length 300 cm, Diameter 3 mm
(d) Length 50 cm, Diameter 0.5 mm

Ans. (d)

Ques: When a uniform wire of radius r is stretched by a 2kg weight, the increase in its length is 2.00 mm. If the radius of the wire is r/2 and other conditions remain the same, the increase in its length is
(a) 2.00 mm
(b) 4.00 mm
(c) 6.00mm
(d) 8.00 mm

Ans. (d)

Ques: Stress to strain ratio is equivalent to
(a) Modulus of elasticity
(b) Poission’s Ratio
(c) Reyhold number
(d) Fund number

Ans. (a)

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(a) 4 mm
(b) 16 mm
(c) 1 mm
(d) 0.25 mm

Ans. (c)

Ques: The modulus of elasticity is dimensionally equivalent to
(a) Surface tension
(b) Stress
(c) Strain
(d) None of these

Ans. (b)

Ques: The ratio of the lengths of two wires A and B of same material is 1 : 2 and the ratio of their diameter is 2 : 1. They are stretched by the same force, then the ratio of increase in length will be
(a) 2 : 1
(b) 1 : 4
(c) 1 : 8
(d) 8 : 1

Ans. (c)

Ques: The extension of a wire by the application of load is 3 mm. The extension in a wire of the same material and length but half the radius by the same load is
(a) 12 mm
(b) 0.75 mm
(c) 15 mm
(d) 6 mm

Ans. (a)

Ques: To keep constant time, watches are fitted with balance wheel made of
(a) Invar
(b) Stainless steel
(c) Tungsten
(d) Platinum

Ans. (a)

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Ques: A copper wire and a steel wire of the same diameter and length are connected end to end and a force is applied, which stretches their combined length by 1 cm. The two wires will have
(a) Different stresses and strains
(b) The same stress and strain
(c) The same strain but different stresses
(d) The same stress but different strains

Ans. (d)

Ques: Two wires ‘A’ and ‘B’ of the same material have radii in the ratio 2 : 1 and lengths in the ratio 4 : 1. The ratio of the normal forces required to produce the same change in the lengths of these two wires is
(a) 1 : 1
(b) 2 : 1
(c) 1 : 4
(d) 1 : 2

Ans. (a)

Ques: The elastic limit for a gas
(a) Exists
(b) Exists only at absolute zero
(c) Exists for a perfect gas
(d) Does not exist

Ans. (a)

Ques: When compared with solids and liquids, the gases have
(a) Minimum volume elasticity
(b) Maximum volume elasticity
(c) Maximum Young’s modulus
(d) Maximum modulus of rigidity

Ans. (a)

Ques: The longitudinal strain is only possible in
(a) Gases
(b) Fluids
(c) Solids
(d) Liquids

Ans. (c)

Ques: The force constant of a wire does not depend on
(a) Nature of the material
(c) Length of the wire
(d) None of the above

Ans. (d)

Ques: The Young’s modulus of a wire of length L and radius r is Y N/m2. If the length and radius are reduced to L/2 and r/2, then its Young’s modulus will be
(a) Y/2
(b) Y
(c) 2Y
(d) 4Y

Ans. (b)

Ques: Longitudinal stress of 1 km/mm2 is applied on a wire. The percentage increase in length is (Y = 1011 N/m2)
(a) 0.002
(b) 0.001
(c) 0.003
(d) 0.01

Ans. (b)

Ques: Why the spring is made up of steel in comparison of copper
(a) Copper is more costly than steel
(b) Copper is more elastic than steel
(c) Steel is more elastic than copper
(d) None of the above

Ans. (c)

Ques: Two wires of copper having the length in the ratio 4 : 1 and their radii ratio as 1 : 4 are stretched by the same force. The ratio of longitudinal strain in the two will be
(a) 1 : 16
(b) 16 : 1
(c) 1 : 64
(d) 64 : 1

Ans. (b)

Ques: Increase in length of a wire is 1 mm when suspended by a weight. If the same weight is suspended on a wire of double its length and double its radius, the increase in length will be
(a) 2 mm
(b) 0.5 mm
(c) 4 mm
(d) 0.25 mm

Ans. (b)

Ques: When a certain weight is suspended from a long uniform wire, its length increases by one cm. If the same weight is suspended from another wire of the same material and length but having a diameter half of the first one then the increase in length will be
(a) 0.5 cm
(b) 2 cm
(c) 4 cm
(d) 8 cm

Ans. (c)

Ques: When a certain weight is suspended from a long uniform wire, its length increases by one cm. If the same weight is suspended from another wire of the same material and length but having a diameter half of the first one then the increase in length will be
(a) 0.5 cm
(b) 2 cm
(c) 4 cm
(d) 8 cm

Ans. (c)

Ques: A and B are two wires. The radius of A is twice that of B. They are stretched by the some load. Then the stress on B is
(a) Equal to that on A
(b) Four times that on A
(c) Two times that on A
(d) Half that on A

Ans. (b)

Ques: If the temperature increases, the modulus of elasticity
(a) Decreases
(b) Increases
(c) Remains constant
(d) Becomes zero

Ans. (a)

Ques: Hook’s law defines
(a) Stress
(b) Strain
(c) Modulus of elasticity
(d) Elastic limit

Ans. (c)

Ques: A wire is loaded by 6 kg at its one end, the increase in length is 12 mm. If the radius of the wire is doubled and all other magnitudes are unchanged, then increase in length will be
(a) 6 mm
(b) 3 mm
(c) 24 mm
(d) 48 mm

Ans. (b)

Ques: The material which practically does not show elastic after effect is
(a) Copper
(b) Rubber
(c) Steel
(d) Quartz

Ans. (d)

Ques: If the temperature increases, the modulus of elasticity
(a) Decreases
(b) Increases
(c) Remains constant
(d) Becomes zero

Ans. (a)

Ques: If Young’s modulus of iron is 2 x 1011 N / m2 and the interatomic spacing between two molecules is 3 x 10–10 metre, the interatomic force constant  is
(a) 60 N/m
(b) 120 N/m
(c) 30 N/m
(d) 180 N/m

Ans. (a)

Ques: A and B are two wires. The radius of A is twice that of B. They are stretched by the some load. Then the stress on B is
(a) Equal to that on A
(b) Four times that on A
(c) Two times that on A
(d) Half that on A

Ans. (b)

Ques: If the length of a wire is reduced to half, then it can hold the _ load
(a) Half
(b) Same
(c) Double
(d) One fourth

Ans. (b)

Ques: The spring balance does not read properly after its long use, because
(a) The elasticity of spring increases
(b) The elasticity decreases
(c) Its plastic power decreases
(d) Its plastic power increases

Ans. (b)

Ques: Two wires of equal lengths are made of the same material. Wire A has a diameter that is twice as that of wire B. If identical weights are suspended from the ends of these wires, the increase in length is
(a) Four times for wire A as for wire B
(b) Twice for wire A as for wire B
(c) Half for wire A as for wire B
(d) One-fourth for wire A as for wire B

Ans. (d)

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Ques: Why the spring is made up of steel in comparison of copper?
(a) Copper is more costly than steel
(b) Copper is more elastic than steel
(c) Steel is more elastic than copper
(d) None of the above

Ans. (c)

Ques: Increase in length of a wire is 1 mm when suspended by a weight. If the same weight is suspended on a wire of double its length and double its radius, the increase in length will be
(a) 2 mm
(b) 0.5 mm
(c) 4 mm
(d) 0.25 mm

Ans. (b)

Steel and copper wires of same length are stretched by the same weight one after the other. Young’s modulus of steel and copper are 2 x 1011 N/m2 and 1.2 x 1011 N/m2. The ratio of increase in length
(a) 2/5
(b) 3/5
(c) 5/4
(d) 5/2

Ans. (b)

Ques: A force F is needed to break a copper wire having radius R. The force needed to break a copper wire of radius 2R will be
(a) F/2
(b) 2F
(c) 4F
(d) F/4

Ans. (c)