• The?power?of a lens is a measure of its ability to?refract?light
  • The?more?refraction a lens causes, the?higher?its power

• The?power?of a lens measures how strongly it focuses the light
  • The?more?curved the lens, the?shorter?the focal length
  • The?shorter?the focal length, the?greater?the power of the lens

• The?power?of a lens is related to:
  • The?focal length?of the lens
  • The?shape?of the lens

The power of a lens depends on its focal length

Calculate the power of a lens

• The power of a lens,?P?is calculated using the following equation:

• Where:
  • P?= power (dioptres, D)
  • f?= focal length of the lens (m)

• Power?is?inversely proportional to?focal length
• For a?concave mirror, where the focal length is negative, power has a negative value

Step 1: Write the known quantities in S.I. units

• • Image is in focus, so the screen is at the focal point
  • Focal length, ?= 60 cm = 0.6 m

Step 2: Write the equation for power and substitute the values

Step 3: Give the full answer, to correct significant figures and with units

??????The power of the lens,?P?= 1.7 D