P14 - Light

Question 1

In general, what is the purpose of a lens?

Answer 1

to form an image by refracting light from a particular object

Question 2

What is the difference between a convex and a concave lens?

Answer 2

-convex curves outwards, and can produce a real or virtual image
-concave curves inwards, and can only produce a virtual image

Question 3

Draw the ray-diagram symbol for a convex and a concave lens:

Answer 3

Question 4

What is the equation for magnification?

Answer 4

Question 5

Give the names of all the features on a ray diagram:

Answer 5

-object
-principal focus (+F2)
-parallel ray
-centre ray
-focal ray
-image

-convex/concave lens
-optical axis

DRAW ARROWS TOO (from object going into lens)

Question 6

How do you draw a ray diagram for a concave lens? How would this be different for a convex lens?

Answer 6

-draw centre ray
-draw a parallel ray, but trace its line back to the principal focus on the side that the object is on using a dashed line
-continue the refracted ray as normal

convex - repeat steps but parallel ray passes through F on other side

Question 7

What is focal length?

Answer 7

distance from the lens to the principal focus

Question 8

Name and describe the different types of reflection:

Answer 8

specular - reflection from a smooth surface in a single direction

diffuse - reflection from a rough surface that causes scattering

Question 9

How do colour filters work?

Answer 9

absorbs certain wavelengths of light whilst transmits others

Question 10

What is the colour of an opaque object determined by? Give an example:

Answer 10

-determined by which wavelengths are more strongly reflected (the rest are absorbed)

-an apple appears red because it only reflects red light whilst absorbing the rest

Question 11

RP9 - How can you investigate the reflection and refraction of light with different surfaces and substances?

Answer 11

-slot collimating slit into ray box and turn on to get a thin light ray
-place the glass block on graph paper and trace around it
-draw a normal, and align the ray to the meeting point
-draw all rays (incident, reflected, refracted)
-label angles (describe what they are in relation to the normal in a question)

Question 12

RP9 - Why should the light ray from the ray box be as thin as possible?

Answer 12

it is harder to judge where the centre of a wider ray is, causing a larger uncertainty in the measurements