Chapter 19: Light

Question 1

What type of waves are light waves?

Answer 1

Transverse waves

Question 2

What can happen to light waves?

Answer 2

They can be reflected, refracted and diffracted.

Question 3

What is reflection?

Answer 3

Light hitting a reflective surface will ‘bounce’ back from the surface.

Question 4

What is refraction?

Answer 4

Light waves changer speed when they pass through objects of different densities, this caused them to change direction.

Question 5

What is diffraction?

Answer 5

When light meets a barrier, it will carry on through the gap, and spread out in be area beyond.

Question 6

What type of waves are light waves?

Answer 6

Transverse waves

Question 9

What is the relationship between the angle of incidence and the angle of reflection when a wave is reflected?

Answer 9

The angle of incidence is equal to the angle of reflection.

Question 10

When are images formed?

Answer 10

Light rays have crossed, and therefore, an image has been created.

Question 11

Describe the difference between a real image and a virtual image

Answer 11

Virtual images are not real. They are laterally inverted and upright. They are the same distance from the mirror or lens as the real image, and they are the same size as it.

Question 12

What is the relationship between the critical angle and the refractive index?

Answer 12

sin(critical angle) = 1/refractive index

Question 13

How do you construct ray diagrams to illustrate the formation of a virtual image in a plane mirror?

Answer 13

Mirror is a straight line with diagonal lines off the back. Incident ray is the lone with arrow pointing towards the mirror, and reflection ray is the same, but with the arrow pointing away.
Extend the reflection ray with a dotted line. Take a couple of rays to form the image in the correct place - where they cross.

Question 14

Describe an experiment to investigate the refraction of light, using rectangular blocks, semi-circular blocks and triangular prisms.

Answer 14

Place a block of glass on a piece of paper, and draw the outline. At one point draw the normal line. Draw a line at 30 degrees to the normal line, shine a ray of light down this line. Draw a line where the light comes out the other side. Connect the two lines, drawing the refracted ray. Measure the angle of the emergent ray. Repeat for different angles, and for different shapes of glass.

Question 15

Describe an experiment to determine the refractive index of glass, using a glass block.

Answer 15

Shine a ray of light through a glass block, measure the angle of incidence and the angle of refraction. Divide sin(angle of incidence) by sin(angle of refraction) and voila, the refractive index of glass!

Question 16

What is the critical angle?

Answer 16

The critical angle is the angle of incidence above which total internal reflection occurs.

Question 17

What is the relationship between the refractive index, angle of incidence and angle of refraction?

Answer 17

Also known as Snell’s Law:

Refractive index = sin(angle of incidence) / sin(angle of refraction)

Question 18

How is total internal reflection used in transmitting information through optical fibres and in prisms?

Answer 18

Beyond the critical angle, light will be reflected back into the medium key came from at the same angle. In this way, they are trapped in the medium. By reflecting light past it’s critical angle, you can make it travel through a medium to send information; this is what happens in prisms and optical fibres.