Lenses

Question 1

Types of lenses

Answer 1

Converging (convex)

Diverging (concave)

Question 2

Lenses formula + magnification formula

Answer 2

1/f = 1/u + 1/v

m= v/u

real images - v = positive
virtual images - v = negative

converging f = positive
diverging f = negative

Question 3

Power of a lens formula

Answer 3

power = 1/focal length in metres

p = 1/f

(dont forget to turn into metres before putting into formula)

Question 4

Two lenses in contact

Answer 4

If two lenses of power P₁ and P₂ are placed in contact, the power P of the combination is given by:

P = P₁ + P₂ and 1/f = 1/f₁ + 1/f₂

Question 5

The eye

Answer 5

Lenses can be used to compensate for defect in human eye

When eye is relaxed, distance from lens to retina is equal to focal length oflens

Question 6

Accommodation

Answer 6

The ability of the ciliary muscle to shorten when an object moves closer

Question 7

Near point

Answer 7

When object is 25cm from eye, it can’t accommodate anymore, this is called near point

Question 8

Myopia

Answer 8

Short sight is when eyebal is too long

Question 9

Hypermetropia

Answer 9

When eyeball is too short, long sightedness

Question 10

Power of a lens

Answer 10

Power is measured in dioptres / m-1 (per metres)

Power of converging lens is positive
Power of diverging lens is negative

Question 11

Contact lenses

Answer 11

1. Stay in place due to surface tension between lens + tears surrounding area
2. Give better all-round vision than glasses
3. Magnifying glass is a converging lens of short focal length

Question 12

A concave mirror can be used to produce an upright image. Why is this not of use if we’re trying to produce an image

Answer 12

virtual image

cannot be formed on a sheet

Question 13

power of converging and diverging lens

Answer 13

Converging lenses have positive optical power, while diverging lenses have negative power