Thin Lens Formula

Linear Magnification

by Ms Wong

​Linear Magnification

Ratio of image height to object height ​

​Linear Magnification

Ratio of image height to object height ​

Multiple Choice

What is the linear magnification when v = 36cm, u = 18cm?

• 2

• 1/2

Multiple Choice

Is the image in earlier magnified or diminished?

• magnified

• diminised

Thin Lens Formula

by Ms Wong

​Thin formula gives the relationship between object distance, u and image distance, v and focal length, f for a lens as:

​

​Sign convention for lens formula

Multiple Choice

focal length of 12cm

• Convex lens

• Concave lens

Multiple Choice

object distance of 16cm

• Convex lens

• Concave lens

Multiple Choice

focal length of -30cm

• Convex lens

• Concave lens

Multiple Choice

image distance of -20cm

• Convex lens

• Concave lens

Multiple Choice

Characteristics with image distance of -30cm

• Virtual, upright

• Real, inverted

​Let's work on a problem solving

Multiple Choice

Which is the correct formula for thin lens?

• $$\frac{1}{f}+\frac{1}{u}=\frac{1}{v}$$  

• $$\frac{1}{u}-\frac{1}{v}=\frac{1}{f}$$  

• $$\frac{1}{f}-\frac{1}{u}=\frac{1}{v}$$  

Multiple Choice

Focal length of a convex lens is 10cm. Determine the image distance if the object distance is 14cm

• 30cm

• 35cm

• 45cm

• 53cm

Multiple Choice

Focal length of a concave lens is 12cm. Determine the linear magnification when the object distance is 4cm.

• 0.57

• 0.72

• 0.75

• 0.78