Topic 5- Light and the electromagnetic spectrum + Flashcards
What is total internal reflection?
-Light from a dense medium to a less dense medium
-Being only reflected back through the semi circular glass block
What happens if incidence > the cirtcal angle
-All light is reflected
What happens if incidence = the cirtcal angle
-Some light is reflected
-Some skims across boundary
What happens if incidence < the cirtcal angle
-Some is reflected
-Some is transmitted/ refracted
What colours are seen through a coloured filter?
-All white objects appear the same colour as the filter
-All other colours are absorbed, so only that filter colour wll be visible, the rest will be black
What are two types of reflection?
Specular- Smooth
Diffuse- Rough
What are the two types of lenses?
-Convex —-> (converge)
-Concave >—-< (diverge)
What is the focal length
Distance between centre of lense to the focal point produced
How to increase focal length?
-Less curved
-Thinner lense
Where is the focal point?
-Both sides of lens
-All horizontal rays meet
What is the power of a lense?
-Opposite of the focal length
-Use a thicker lense
What can an image be?
-Real vs Virtual
-Magnified vs Diminished
-Upright vs Inverted
What is a real vs virtual image?
Real = Inverted (projected onto a screen)
Virtual = Upright image
What produces real images?
Convex
What produces virtual images?
-Convex
-Concave
How to draw a ray diagram for concave?
1) Choose one point that is parallel into focal point (for concave draw imaginary line to focal point and continue past the lense)
2) Choose one point that goes through centre (won’t be refracted)
3) Find where they cross (for concave on the same side as the object)
How to draw a ray diagram for convex?
1) Choose one point that is parallel (goes through focal point on other side)
2) Choose one point that goes through centre (won’t be refracted)
3) Find where they cross (for convex on the other side as the object)
What are electromagnetic waves?
-Transverse waves
-Can travel through a vacumm at the same speed
What do electromagnetic waves transfer?
-Energy from source to observer
-E.g light
Core Practical: Investigate refraction in rectangular glass blocks in terms of the interaction of electromagnetic waves
with matter
1) Place on paper
2) Draw around glass block
3) Thin beam of light onto paper using a ray box and slit
4) Draw the rays of incidence and refraction
5) Use a protractor to measure
What are the electromagnetic waves from longest to shortest?
-Radio
-Microwave
-Infrared
-Visible light
-Ultra violet
-X-ray
-Gamma
What do different substances do?
-Transmit, absorb and refract different waves differently due to wavelength
Why do waves refract?
-Frequency remains to the same
-But wavespeed changes
-wavelength must change
-Light is slower in denser mediums so bends towards the normal
bends towards or away from the normal
What do objects above absolute 0 do?
-Emmit raditation
-The hotter the object, the shorter wavelength radiation it emits
Why are objects at constant temperatures?
-They absorb radiation at the same avg power that they emit it
What happens if an object absorbs more or less radiation that it emits?
-Gets hotter
-Gets cooler
What does the Earth’s temperature depend on?
-Balance between incoming radiation from the sun and emition
-Sun emits short length radiation (mostly visible light)
-Earth emmits longer wave length radiation back to space
-Some is absorbed by greenhouse gasses, heating the Earth further
Core Practical: Investigate how the nature of a surface affects the amount of thermal energy radiated or absorbed
1)Cover boiling tubes with different material
2)Add hot water
3)place thermometre to
4)measure temperature change every 2 minutes
5)Plot on a graph
Which electromagnetic waves are more dangerous?
-Higher frequency
Harmful effects of microwaves?
-Internal heating of body tissue
Harmful effects of infrared?
Skin burns
Harmful effects of visible light?
-Blue light can damage retina in the eye
Harmful effects of UV?
-Ionising so can cuase skin cancer
-Eye cateracts
Harmful effects of X-ray and gamma?
-Ionising damage DNA
-Cuases cancer
What are radio waves used for?
-Broadcasting, communications and satellite transmissions
Longest wavelength (arn’t absorbed by atmosphere)
What are microwaves used for?
-Cooking, communications and satellite transmissions
-Absorbed -> H2O molecules= vibration+ heat
-Some absorbed by atmosphere
What are infrared waves used for?
-cooking, thermal imageing, short range communications, television remote, security systems
What are visible light waves used for?
-Pictures
-Seeing
-Illumination
What are UV waves used for?
-Security marking, flourescent lamps, detecting money forgery, tanning, disenfecting water
What are X-rays used for?
-Internal structure
-Airport security
-Medical X-rays
absorbed by bone not by tissue
What are gamma rays used for?
-Sterilising medical areas and food
-Detection of cancer and its treatment
What produces radio waves and what do they produce?
-Oscillations in metal aerials/ electrical circuits
What can the change in an atoms nuclei cuase?
-Generate radiation over a wide frequency rate
-Can be cuased by absorbed of radiation (excitation)
