Physics : Properties of Matter : Book Back Choose the correct Answers with Solution, One Mark and Multiple choice questions with Answers and Solution

__Properties of Matter (Physics)__

__Multiple Choice Questions__

**1. Consider two wires X and Y. The radius of wire X is 3 times the radius of Y. If they are stretched by the same load then the stress on Y is**

(a) equal to that on X

(b) thrice that on X

(c) nine times that on X

(d) Half that on X

**Answer : c) nine times that on X**

**Solution:**

σ_{x} ∝ 1 / r_{x}^{2 };

σ_{y} ∝ 1 / r_{y}^{2}

σ_{x} / σ_{y }= (r_{y} / r_{x })^{2
}= (r_{y} / 3r_{y })^{2}

σ_{x} / σ_{y }= (1/3)^{2} = 1 / 9

σ_{y} = 9 σ_{x}

**2. If a wire is stretched to double of its original length, then the strain in the wire is**

(a) 1

(b) 2

(c) 3

(d) 4

**Answer : a) 1 **

**Solution:**

ε = Δ*l* / *l*

ε = [ *l*_{t }– *l _{o}* ] /

*=* (2 – 1) / 1 = 1 / 1 = 1

**3. The load – elongation graph of three wires of the same material are shown in figure. Which of the following wire is the thickest?**

(a) wire 1

(b) wire 2

(c) wire 3

(d) all of them have same thickness

**Answer : a) wire 1 **

**Solution:**

If slope is high the elongation will be less

**4. For a given material, the rigidity modulus is (1/3) rd of Young’s modulus. Its Poisson’s ratio is**

(a) 0

(b) 0.25

(c) 0.3

(d) 0.5

**Answer : d) 0.5**

**Solution:**

η = 1/3 *y *

*y = *2 η (1 + μ )

*y* = 2*y*/3 (1 + μ )

3/2 = 1 + μ

μ = (3/2) – 1 = 1 / 2

μ = 0.5

**5. A small sphere of radius 2cm falls from rest in a viscous liquid. Heat is produced due to viscous force. The rate of production of heat when the sphere attains its terminal velocity is proportional to**

(a) 22

(b) 23

(c) 24

(d) 25

**Answer : d) 2 ^{5}**

**Solution:**

*dQ* / *dt* = *E* / *t* =
*Power*

*Power* = P = *F* × v_{t}

F = 6πη*r*v_{t}

*dQ* / *dt* = 6πη*r*v_{t}^{2}

*v _{t} *= [2/9] [ (ρ – σ )
/ η]

*dQ* / *dt* = 6πη*r* × ( 2/9 [
(ρ–σ)/η × *g* ])^{2} × *r*^{4}

*dQ* / *dt* ∝ *r*^{5}

**6. Two wires are made of the same material and have the same volume. The area of cross sections of the first and the second wires are A and 2A respectively. If the length of the first wire is increased by ∆ l on applying a force F, how much force is needed to stretch the second wire by the same amount?**

(a) 2

(b) 4

(c) 8

(d) 16

**Answer : b) 4 F**

**Solution:**

*y* = *Fl* / [Δ*l* × *A*]

*y* = [ *Fl* / *A*Δ*l* ]
× [ *A */ *A* ] = [*F.V *]
/ [Δ*l* × *A*^{2}]

*F* ∝ *A*^{2}

*F*_{2} / *F*_{1 }= [ (2*A*)^{2} ] / [*A*^{2
}] = 4

*F*_{2 }= 4* F*_{1}

**7. With an increase in temperature, the viscosity of liquid and gas, respectively will**

(a) increase and increase

(b) increase and decrease

(c) decrease and increase

(d) decrease and decrease

**Answer : c) decrease and
increase**

**8. The Young’s modulus for a perfect rigid body is**

(a) 0

(b) 1

(c) 0.5

(d) infinity

**Answer : d) infinity**

**Solution:**

*Y*** **= *Fl*
/ Δ*lA *= *Fl* / [*O × A*]*
*= *Fl* / *O*

*Y*** **= ∞

**9. Which of the following is not a scalar?**

(a) viscosity

(b) surface tension

(c) pressure

(d) stress

**Answer : d) stress**

**10.**** If the temperature of the wire is increased, then the Young’s modulus will**

(a) remain the same

(b) decrease

(c) increase rapidly

(d) increase by very a small amount

**Answer: b) decrease**

**Solution: **

*Y*** **= (*Fl*) / (*A.*Δ*t*)* *

⇒* *Y ∝ 1 / Δ*t *

**11. Copper of fixed volume V is drawn into a wire of length l. When this wire is subjected to a constant force F, the extension produced in the wire is ∆l. If Y represents the Young’s modulus, then which of the following graphs is a straight line?**

(a) ∆l verses V

(b) ∆l verses Y

(c) ∆l verses F

(d) ∆l verses 1/l

**Answer: c) Δ l versus F**

**Solution: **

*Y*** **= (*Fl*
) / (*A.* Δ*l*)* *=
*Fl* / *V*

**12. A certain number of spherical drops of a liquid of radius R coalesce to form a single drop of radius R and volume V. If T is the surface tension of the liquid, then**

(d) energy is neither released nor absorbed

**Answer : c) energy = 3VT [
1/r – 1/R ] is released**

**13. The following four wires are made of the same material. Which of these will have the largest extension when the same tension is applied?**

(a) length = 200 cm, diameter = 0.5 mm

(b) length= 200 cm, diameter = 1 mm

(c) length = 200 cm, diameter = 2 mm

(d) length= 200 cm, diameter = 3 m

**Answer : a) length = 200 cm, diameter = 0.5 mm**

**Solution:**

Δ*l *= *Fl* / *AY *= *Fl* / π*r*^{2}*Y*

Δ*l* ∝ *l* / *r*^{2} ,

Δ*l **∝** l* / *d*^{2}

**14.**** The wettability of a surface by a liquid depends primarily on**

(a) viscosity

(b) surface tension

(c) density

(d) angle of contact between the surface and the liquid

**Answer : d) angle of
contact between the surface and the liquid**

**15. In a horizontal pipe of non-uniform cross section, water flows with a velocity of 1 m s-1 at a point where the diameter of the pipe is 20 cm. The velocity of water (m s-1) at a point where the diameter of the pipe is**

(a) 8

(b) 16

(c) 24

(d) 32

**Answer : b) 16**

**Solution:**

a_{1}v_{1} = a_{2}v_{2}

*π* [d_{1}^{2}v_{1}
/ 4] = *π* [d_{2}^{2}v_{2} / 4] . v^{2}

d_{2}^{2 }= [v_{1 }/ v_{2} ] d_{1}^{2}

= (1/1.5) × 400 × 10^{-4}

= 2.66 × 10^{-4}

d_{2}^{ }= 16.3 × 10^{-2}

= 16.3 cm

Tags : Properties of Matter | Physics , 11th Physics : UNIT 7 : Properties of Matter

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