Question

Ques 1) A real image 1/5th the size of object is formed at a distance of 18 cm from a mirror . What is the nature of morror ? Calculate its focal length.

Ques 2 )A student has two resistor 2 ohm and 2 ohm . She has to put one of them in place of R2 as shown in the circuit . The cirrent that she needs in the entire circuit is exactly 9A . Show by calculation which of the two resistor she should choose ?​

Answer 1

Answer:

Answer

Given: a real image is

5

1

th

the size of the object, and it is formed at a distance of 18cm from the mirror.

To find the focal length of the mirror and the nature of the mirror.

Solution:

According to the given criteria,

image distance, v=−18cm

magnification, m=−

5

1

as the image formed is real hence it will be inverted.

We know,

m=−

u

v

⟹−

5

1

=−(

u

−18

)

⟹u=−(5×18)=−90cm

Applying the lens formula,

f

1

=

v

1

+

u

1

⟹

f

1

=

−18

1

+

−90

1

⟹

f

1

=

90

−5−1

⟹f=−15cm

Since focal length is negative, therefore it is a concave mirror.

Answer 2

ʏᴏᴜʀ ᴀɴsᴡᴇʀ ɪs ɪɴ ᴀᴛᴛᴀᴄʜᴍᴇɴᴛ.