Question

D. 'g' vanishes at centre of

6) A prism of 6° is made of material of refractive index What is the
deviation caused by it
d. 40
c.120
a. 60
b.8°
7) An object is placed 1cm from lens having magnification 5. Then its foc
length is
a. 0.8 cm b. 1.2 cm c. -1.2 cm d. -0.8cm​

Answer 1

a. 0.8 cm

Step-by-step explanation:

The distance of the object from the lens, u = 1 cm

The magnification of the lens, m = 5

The focus of a lens formula is given as follows;

`f = (1)/((1)/(v) + (1)/(v) )`

The magnification of the lens, m = -v/u

Where;

v = The distance of the image from the lens

Therefore, we have;

v = m × u

∴ v = 5 × 1 cm = 5 cm (on the other side of the lens)

From which we get;

`f = (1)/((1)/(1) + (1)/(5) ) = (5)/(6) \approx 0.8`

The focal length ≈ 0.8 cm