Light

Question 1

What are the four properties of light waves?

Answer 1

They are transverse, and can be reflected, refracted and diffracted.

Question 2

How are the angles of incidence and reflection connected?

Answer 2

angle of incidence = angle of reflection i = r

Question 3

How do you work out the critical angle?

Answer 3

sinC = 1 ÷ n

Question 4

How do you work out the refractive index (n)?

Answer 4

n = sin(i) ÷ sin(r)

Question 5

When light reflects from the surface of a plane mirror, the angle of incidence is the angle of reflection

Answer 5

equal to

Question 6

What type of wave is visible light?

Answer 6

Transverse.

Question 7

How is an image formed in a plane mirror?

Answer 7

Question 8

What is the difference between a virtual and a real image?

Answer 8

A virtual imaging is formed from diverging rays, which do not actually meet at the image.

Question 9

What is the critical angle?

Answer 9

The angle of incidence when the angle of reflection is equal to 90º and above which no light can pass through a surface so you get total internal reflection.

Question 10

How could you find the refractive index of light using a glass block?

Answer 10

• Draw around a rectangular glass block and direct a ray of light through it at an angle.
• Trace the incident and emergent rays.
• Remove the block and draw in the refracted ray.
• Use a protractor to measure the angle of incidence and the angle of reflection.
• Calculate the refractive index using Snell’s law: n=sin(i)÷sin(r).

Question 11

How do you investigate the refraction of light using rectangular blocks, semicircular blocks and triangular prisms?

Answer 11

• Place a glass block on a pice of paper and trace around it.
• Shine a light at the block and draw where the line goes in and where it comes out.
• Repeat fo different shapes of glass.

Question 12

Which is the angle of incidence and which is the angle of reflection?

Answer 12

a) Angle of reflection
b) Angle of incidence

Question 13

What are the conditions required for total internal reflection to happen?

Answer 13

• The angle of incidence must be greater than the critical angle.
• The light ray must be travelling from a more opitcally dense to a less optically dense medium.

Question 14

What are the advantages of sending signals using optical fibres instead of electrical currents in copper wires?

Answer 14

• Less prone to noise.
• Less prone to heating.
• More information can be sent per second.
• More data can be sent per second.

Question 15

What is a propety of the cladding in optical fibres?

Answer 15

The core is surrounded by cladding with a lower refractive index.

Question 16

Why is the core of an optical fibre narrow?

Answer 16

So that light hits the core-cladding boundary at an angle higher than the critical angle (c) and light is always totally internally reflected.

Question 17

What is happening to the light in this glass fibre?

Answer 17

Total internal reflection:

Light reflects inside the surface off the fibre because the angle of incidence is greater than the critical angle because of the fact that light travels slower in glass.

Question 18

What are some uses of total internal reflection?

Answer 18

• Optical fibres for communication.
• Endoscopes.
• Optical fibres in decorative lamps.
• Safety reflectors (e.g. cat’s eye).