A 5cm pencil is placed at a distance of 20cm from a converging mirror with a focal length of 40cm. i) using formulas, calculate the distance to the image. ii) calculate the image height.

Question

iii) find the magnification factor.

Answer 1

Hi Blue C.,

Use the mirror equation 1/d₀ +1/d_i = 1/f with f = 40 cm, d₀ = 20 cm:

1/d_i = 1/40 - 1/20 = -1/40, therefore d_i = -40 cm. The minus sign means the image is behind the mirror.

Use h_o/h_i = d_o/d_i, h_o = 5*20/-40 = -2.5 cm.

For magnification use m = -d_i/d_o = -(-40)/20 = +2. So the image is twice as large and upright.

I hope this helps, Joe.