jamb 2020 physics questions and answers page 3

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11. 

In what range of temperature is the expansion of water anomalous?

A 

+208C to +212C

B 

-80C + -76C

C 

0C to +4C

D 

-4C to +0C

correct option: C

 explanation:

The anomalous expansion of water is an abnormal property of water whereby it expands instead of contracting when the temperature goes from 0C to +4C, and it becomes less dense

12. 

Which of the following conditions are necessary and sufficient for total internal reflection to take place at the boundary between two optical media?

I. 

Light is passing from optical denser medium to optically less dense medium

II. 

Light is passing from optically less dense medium to optically denser medium

III. 

Angle of incidence is greater than a certain critical value

IV. 

Angle of incidence is lesser than a certain critical value

 

A. 

I and II only

B. 

II only III only

C. 

III and IV only

D. 

I and III only

correct option: B

 explanation:

The conditions for total internal reflection include light traveling from an optically denser medium (higher refractive index) to an optically less dense medium (lower refractive index) and that the angle of incidence is greater than the critical angle.

13. The linear expansivity of brass is 2 x 10-5C-1. If the volume of a piece of brass is 15.00cm3 at 00C, What is the volume at 100oC?

A. 16.03cm3

B. 16.00cm3

C. 15.09cm3

D. 15cm3

correct option: A

explanation:

3 x = 

3 x 2 x 10 = 

V = (100 x 10 x 3 x 2 10) + 10

= 10.6 cm

14. Consider the three forces acting at O and in equilibrium as shown in the figure. Which of the following equations is/are CORRECT?

I. P sin = p cos 

II. P = P cos + P

III. P

A 

I only

B 

II only

C 

III only

D 

I, II and III only

correct option: C

 explanation:

From ABC

P = P cos 

From ACD

P = P cos

P cos  

PCos   

15. A convex mirror is used as a driving mirror because 

I. its image is erect     

II. It has a large field of view

III. It has a long focal length 

Identify the CORRECT statement(s) 

A 

I and III only

B 

I and II only

C 

II and IIII only

D 

I, II and III only

correct option: C

 explanation:

(A) R = 2 + 3 + 6 = 11 

(B) R = 

  = 1.2

(C) R =

= 1 

(D) R = 3 + 

= 4.5  

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