## 08 November 2014

### Physics - Class 10 - to study refraction of light in rectangular glass slab

In triangle GBC, r1+90 =-r2+90 ...as the sum of angles in a triangle is 180 degree

r1=r2............................i

Now refractive index of glass=sin i/sin r1 =sin e/sin r2....................ii

as r1=r2 from (i)

so i=e .................iii

Now as the incident ray is extended till E, angle LDE should be equal to i.

For, CF and DE, and interceptor CD angle BCF(90+e)=angle CDE(90+i) and they are corresponding angle so CF parallel to DE.

1) A ray of light incident on one of the parallel faces of a rectangular glass slab, emerges out of the opposite parallel face

a)      parallel to the incident ray but laterally displaced
b)      inclined to the incident ray
c)       along the same straight line as the incident ray
d)      gets absorbed into the body of the glass slab and does not emerge out of it

2) Four students reported the following observation tables for the experiment to trace the path of a ray of light passing through a glass slab for different angles of incidence. The observations, likely to be correct are those of student.

 ∠i ∠r ∠e ∠i ∠r ∠e 30 40 30 30 20 30 40 50 40 40 30 40 50 60 50 50 40 50 (a) (b) ∠i ∠r ∠e ∠i ∠r ∠e 30 20 40 30 20 20 40 30 50 40 30 30 50 40 60 50 40 40 (c) (d)

(a) A                     (b) B                      (c) C                       (d) D

3) Why does bending of light takes place ?

a)      Because light travels with same velocity in different media
b)      Because it travels with different velocity in different media
c)       None of these

4) In which direction does a ray bend when it travels from a denser medium to a rarer medium :

a)      It bends away from the normal as it meets the surface of rarer medium
b)      It bends towards the normal as it meets the surface of rarer medium
c)       It goes straight
d)      None of these

5) Refractive index is the property of :

a)      One medium
b)      The pair of media
c)       One vacuum
d)      None of these

6) Does the refractive index of substance change with the colour of light ?

a)      No, refractive index does not depend upon the colour of light (wavelength)
b)      Yes, refractive index depends upon the colour of light (wavelength)
c)       None of these

7) Give the example of total internal reflection :

a)      Mirage (Mrig Trishna), generally observed in deserts in summer
b)      Looming, generally observed in cold region
c)       Both of these

8) What is critical angle ?

a)      Critical angle is the angle of incidence for which angle of refraction is 45 degree when light travels from denser medium to rarer
b)      Is the angle of incidence for which angle of refraction is 90 when light travels from rarer to denser medium
c)       Is the angle of incidence for which angle of refraction is 90 when light travels from denser to rarer medium
d)      None of these

9) What is the advantage of "total internal reflection" over reflection ?

a)      Total internal reflection is an interesting phenomenon than reflection
b)      Loss of intensity of light is less in total internal reflection than reflection
c)       None of these

10) What do you mean by the statement "Refractive Index of glass is 1.5"

a)      It means refractive index of glass with respect to air is 1.5
b)      Refractive index of air with respect to glass is 1.5
c)       It means refractive index of glass with respect to water is 1.5
d)      None of these