Lenses

What are the two types of lens

Concave and Convex Lens

How is the symbol for convex lens and what is their shape

Describe convex lens thcikness

Thicker at centre then edges

What do all lenses do

They refract light to from images

What is the principal focus in a convex lens

Where rays hitting the lens parallel to the axis meet

What is the focal length

The distance from the centre of the lens to the principal focus

What is the Axis of a Lens

A line passing through the middle of lens, perpendicular to the lens

What are the three Rules for Refraction in a Convex Lens

1)An Incident ray parallel to the axis refracted through the lens and passes through the principal focus on the other side

2) An incident ray passing through the principal focus refracts through lens and travels parallel to axis

3)An incident ray passing through the centre of lens carries on in the same direction

Describe how you draw a Ray diagram with convex lens STEP 1

Draw a line from top of the object passing straight through the centre of the lens without changing direction

STEP 2

Draw another line from top of object which runs parallel to principal axis so when it hits lens it’s refracted through the principal focus

STEP 3

Where the two lines meet, shows us top of image

This image is Diminished, inverted and a real image

When you’re describing an image, what are the three things you must talk about

1)How big it is compared to the object(Has it magnified or diminished)

2)Whether it’s upside down or not(Inverted or Upright)

3)Whether it’s Real or Virtual(Real is when all the rays meet at a point. Virtual is when they don’t)

If the object is more than 2 focal lengths from the lens…

Image is diminished

Image is inverted

Image is Real

If object is between 1 and 2 focal lengths from lens then….

Image is magnified

Image id inverted

Image is Real

What is the Concave lens shape and symbol

Describe Concave lens thcikness

Thicker at the edge compared to the center

What happens to light rays once they pass through concave lens

Causes Parallel rays of light to spread out (diverge)

Where is the principal focus on a concave lens

Describe the three rules for the redaction in a concave lens

1)An Incident ray parallel to the axis refracts through the lens and travels in line with the principal focus(so it appears to have come from principle focus)

2)An Incident ray passing through the lens towards the principal focus refracts through the lens and travel parallel to the axis

4)An incident ray passing though the centre of the lens carries on in the same direction

Describe how to draw a ray diagram with a concave lens STEP 1

Draw a ray from the top of the object passing through the centre of the lens without changing the direction

STEP 2

Draw another ray from the top of the object. This passes through the lens and is refracted. This ray must appear to have come from the principal focus so draw a dotted line to show

STEP 3

Where these lines meet shows us the location of the image

Image is diminished

Image is upright

Image is Virtual

So in a Concave lens what three properties will the image always have

Always be diminished, right way up and virtual

Why are concanve lens images virtual

As we can’t see this image on a screen

Describe how to draw a ray diagram for a magnifying glass STEP 1

Object is between 1 focal length and the lens. Start by drawing a ray of light from the top of the object through the centre of the lens

STEP 2

Draw another ray from top of object running parallel with principal axis, this ray passes though the principal focus

STEP 3

Draw dotted lines to extend the rays behind the lens

STEP 4

Where the dotted lines meet shows us us the postion of the image.

-Draw an eye between two rays at bottom

Results should be Image is Magnified, upright and virtual

Why can’t see a virtual image on a screen

As the only time that a convex lens lrucrds a virtual image is when it’s used as a magnifying glass

A magnifying glass is used to view an object which has a height of 0.5cm

The image has a height of 3.5cm

Calculate the magnification

Magnification = 3.5/0.5 =7X

What is Specular reflection

Reflection from a smooth surface in a single direction which produces an image

What if Diffuse Reflection

Reflection from a through surface that doesn’t produce an image

What is white light

A mixture of all the different colours

What happens if we pass white light through a prism

Then it splits into a spectrum

What does the colour of an object depend on

Which wavelengths of light are reflected,transmitted or absorbed

How do colour filters work

They absorbs specific wavelengths and transmitting (Allowing through) other wavelengths

Describe how a red filter would work

1)Shine white light onto the filter

2)The filter then absorbs all the colours of visible light apart from red

3)So only red light transmitted though the filter

Objects that transmit light can be either…

Transparent(Can easily see though object)

Translucent(These objects scatter the light rays so we can’t see though them clearly)

What are Opaque objects

Objects that we cannot see through at all so light can’t pass through

Why do white objects appear white

Because they reflect all of the wavelengths of visible light equally

Why do objects appear black

Because they absorb all the wavelengths of visible light

Why does a object appear red colour

As when white light is shining onto a red object the red object absorbs all all the colours of white light apart from red which is reflected

Why does a red object appear red through a red filter

The Red filter absorbs all the colours of white light apart from red which is transmitted and then red light is reflected off the red object so it appears red

Describe what you’ll see with a green object and a red filter

Red filter allows red light to be transmitted however green object absorbs all the red light so none is reflected so green object will appear black as it is reflecting no light at all

The colour of a opaque object depends on what

Which wavelengths of light are most strongly reflected E.g a red apple appears red because the wavelengths corresponding to the red part of the visible spectrum are most strongly reflected, the others are absorbed

Which surface it the best absober and best emitter of infrared radiation

Matt Black surface

What do all bodies(objects) do

Emit and absorbed infrared radiation

The hotter an object is…

The more infrared radiation is emitted in a given time compared to a cooler object

Both the wavelength and intensity of radiation depend on…

The temperature of the object

What else do very hot objects emit

Short wavelength

As object gets hotter what happens to wavelength and what does it produce

Wavelength gets shorter,producing visible light

An object that’s hotter than its surroundings..

Emits more IR radiation than it absorbed as it cools down(E.g cup of tea on table is warmer than the air around it so it gives out more IR radiation than it absorbs which cools it down)

An object that’s cooler than its surroundings…

Absorbs more IR radiation than it emits as it warms up(E.g cold glass water on a sunny day)

Objects at a constant temperature

Emit IR radiation at the same rate it absorbs its

What is silver surfaces best at and worst at

Best at reflection while being worst for emitting and absorbing.

What is a perfect black body

Absorbs all of the radiation that hits it. No radiation is reflected or transmitted

A perfect black body is all the best…

Possible emitter of radiation

How does the earth gain or lose energy

By absorbing or emitting radiation

What does the sun emit

Short wavelength radiation which travels to Earth

What happens to radiation emitted from sun

Some is sent to the earth

Some is reflected by clouds

Remaining radiation can be absorbed by the surface of the earth causing the temperature of Earth to increase causing the Earth to emit infrared reaction back into space

Why is human activity that increases level of greenhouse gases bad

-Some of the energy of the infrared emitted by Earth is trapped by greenhouses gases in atmosphere like carbon dioxide meaning more heat energy is trapped in the atompshere and less is radiated into space

Why are cloudy nights more warmer than clear nights

As clouds can reflect infrared back to the Earth and prevent it being radiated into space

What factors affect how much energy is radiated from the earth

Cloud cover