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GCSE level optics questions

Q19. One type of digital camera contains both a converging (convex) lens and a diverging (concave) lens.

(a) State the name of the light detector used in digital cameras.

CCD (charge coupled device) or CMOS

[1 mark]

(b) Converging and diverging lenses both produce images.

What type of images can be produced using converging and diverging lenses?

Tick one box for each type of lens.

Converging lens Diverging lens
Real image only   Real image only  
Virtual image only   Virtual image only
Both real and virtual images Both real and virtual images  

[2 marks]

(c) Each lens in the digital camera is made from a different type of glass.

The graph below shows the relationship between the frequency of light and the refractive index of the glass used to make each lens.

Describe three differences between the refractive index of the glass used for the converging lens compared to the glass used for the diverging lens as the frequency of light increases.

The refractive index of the converging lens is greater (for all frequencies) than that of the diverging lens.

The refractive index of the converging lens increases more than that of the diverging lens.

The refractive index of the converging lens reaches a maximum at a lower frequency than that of the diverging lens.

[3 marks]

(d) At one frequency, the glass of the diverging lens has a refractive index of 1.60

The angle of incidence of a ray of this light on the diverging lens is 20°

Calculate the angle of refraction for the ray of light.

n = sin i/sin r

1.60 = sin 20o/sin r

sin r = sin 20o/1.60

sin r = 0.342/1.60 = 0.214

r = 12o

[3 marks]

(e) The focal length of the diverging lens is 40 cm.

Calculate the power of the diverging lens.

Give the unit.

diverging lens (concave lens) has a negative focal length

P = 1/f (but f must be in metres)

P = 1/-0.40

P = - 2.5 dioptres

P = - 2.5 D

 

[4 marks]

(f) Give two factors that affect the power of a lens.

The curvature of the lens and the refractive index of the material it is made of.

[2 marks]

(Total 15 marks)