In order to get the G.C.S.E. grade you are capable of, you must make your own revision notes using your Physics notebook. When summarising notes, use different colours and draw diagrams/pictures. If you do, you will find them easier to remember. Once you have made revision notes for a topic, re-visit these regularly (on the day of your examination you will not remember something you revised 4 weeks previously). Each time you re-visit a note, tick the top of the page/card. This will allow you to identify any notes you have neglected. WARNING: DO NOT RELY SOLELY ON THE REVISION POWERPOINTS!
Smallest energy largest energy Radio waves Microwaves Infra red Visible Ultraviolet X-rays Gamma rays largest wavelength shortest wavelength To help remember the order in decreasing wavelength: Rabbits Mate In Very Unusual expensive Gardens Learn the uses and dangers of each wave!
The Law of reflection states: The angle of incidence = The angle of reflection Click to see
Results The image in a plane mirror is: 1. the same size as the object 2. as far behind the mirror as the object is in front 3. virtual 4. laterally inverted (back to front) Learn how to draw this diagram!! (See next slide)
The image in a plane mirror is as far behind the mirror as the object is in front. By using this fact, we cheat when locating the image: 1. Draw your image in the correct location (as far behind the mirror as the object is in front). Use a ruler to do this accurately! (click to see) 2. Draw two rays from the object to the mirror. (click to see) 3. Reflect these rays as if they originate from the image, dashing the lines behind the mirror. (click to see) 4. Don t forget your arrows!!! Now try this on a blank piece of paper!!!
A periscope is an application of reflection. It is used to see over obstacles. As you can see from the diagram, the image is upright. Ray from the top of an object Object Ray from the bottom of an object Image
Less dense to more dense light slows down More dense to less dense light speeds up Refraction is the bending of light when it goes from one material to another. It occurs because light changes speed.
Less dense - more dense, e.g. air glass: Air (Less dense) Glass (More dense) More dense - Less dense, e.g. glass - air: Glass (More dense) Air (Less dense) Less dense more dense bent towards from the normal More dense less dense bent away from the normal
1. Draw a normal where the ray strikes the surface. (click) 2. Line your ruler up with the incident ray. 3. Draw your refracted ray (see previous page) (click) 4. Continue this ray until it meets another surface and repeat points 1-3. (click) Examples: 1 2 3 air water air water glass air 4 5 air glass glass air
White light is a mixture of the following colours: Red, Orange, Yellow, Green, Blue, Indigo and Violet (ROY G BIV) Each of these colours travels at the same speed in air but different speeds in glass. Therefore, if a ray of white light travels though a prism: On entering the glass each colour slows down by a different amount and is, therefore, refracted by a different amount (click to see) Red light slows down the least refracts the least White light air glass Red O Y G B I Violet Violet light slows down the most refract the most Learn how to draw this diagram!!!
1. When light travels from water to air it is refracted away from the normal (click to see 3 times) 2. As light travels in straight lines, the person believes this light originates from somewhere along the path shown. (click to see) 3. The goggles appear to be located at X. (click to see) air water X goggles
When light travels from an optically more dense to an optically less dense material it is refracted away from the normal. At a certain angle of incidence, called the critical angle, the angle of incidence will be 90 When the angle of incidence is greater than the critical angle the light is reflected total internal reflection. Click to see
For total internal reflection to occur: 1. The light must be going from more dense less dense. 2. The angle of incidence must be greater than the critical angle
Reflecting Prism Communication Medical Imaging
Converging (Convex) Thickest in the middle Diverging (Concave) Thinnest in the middle
F PA O f The Optical Centre (O) of a lens is the centre of the material (glass) of the lens The Principal Axis (PA) of a lens is a line drawn through the centre (O) of the lens and is perpendicular to the lens surfaces. The focal point or focus (F) of a convex lens is the point on the principal axis through which all rays parallel and close to the principal axis are refracted after passing through the lens. The focal length (f) is the distance between the focus and the optical centre.
object 2F F F 2F To draw a ray diagram: 1. Draw a ray from the top of the object and pass this through the optical centre (click to see) 2. Draw a ray parallel to the principal axis and refract this through F (click to see) 3. Draw your image where the two rays meet or appear to meet (click to see)
Click to adjust the position of the object
Object beyond 2f Object at 2f Image is: real, diminished (smaller than object), and inverted (upside down) Image is: real, the same size as the object and inverted Object between 2f and f Object at f Image is: real, the magnified and inverted. Rays are parallel after passing through the lens image is formed at infinity.
When the object is inside f the rays diverge (move away) after passing through the lens. Therefore, the image is virtual (cannot be produced on a screen)
Use Magnifying glass 2F F object F 2F To draw a ray diagram: 1. Draw two rays from the top of the object as normal (click to see) 2. Trace these rays behind the lens using dashed lines (click to see) 3. Draw your image where the two rays appear to meet (click to see)
1. Set the apparatus up as shown 2. Adjust the position of the lens until a sharp image of a distant object ( e.g. the Crombie) is formed on the screen. 3. Measure the distance from the centre of the lens to the screen (i.e. the focal length). 4. Repeat a further two times and calculate an average.
Transverse vibrations perpendicular to direction Longitudinal vibrations parallel to direction
Graphical Representation displacement wavelength distance amplitude wavelength
Wave Equation The wave equation links wave speed, frequency and wavelength. Wave velocity (m/s) = frequency (Hz) x wavelength (m) v = f x
Examples 1. What is the wavelength of a sound wave of frequency 264 Hz and speed 330 m/s? λ = v / f = 330 / 264 = 1.25 m 2. Find the frequency of radio waves of wavelength 1500 m if their speed is 300,000,000 m/s. f = v / λ = 300000000 / 1500 = 200,000 Hz
Wave Fronts Wave fronts are drawn perpendicular to the direction of travel. The separation of adjacent wave fronts is the wavelength of the wave
Answering questions on reflection: 1. Draw in the path of the incident wave. 2. Draw in the path of the reflected wave, remembering i = r. 3. Add wave fronts to the reflected wave, ensuring they have the same separation as the incident wave fronts. Click to see
air glass Click to see water air Remember: 1. Water waves travel faster in deep water than shallow water. 2. Light travels faster in air than glass. 3. Light travels faster in air than water. Answering questions on reflection: 1. Draw in the path of the incident wave. 2. Draw in the path of the refracted wave. 3. Add wave fronts to the reflected wave, ensuring you have spaced them correctly - decrease in speed, decrease in wavelength; increase in speed increase in wavelength
1. Dolphin A sends out a pulse of sound to communicate with dolphin B. The sound takes 0.2 s to travel 300 m from A to B. Calculate the speed of sound in water. speed = distance / time = 300 / 0.2 = 1500 m 2. A golfer uses an ultrasound device to measure the distance to a flag. The device shows the distance to be 82.5 m. If the speed of sound in air is 330 m/s, how long does it take for the sound to travel to the flag and back? distance to flag and back = 2 x 82.5 = 165 m time = distance / speed = 165 / 300 = 0.5 seconds
Click for solutions Ray from head strikes the mirror 5 cm above eye level Ray from chin strikes the mirror 6 cm below eye level Shortest length = 5 + 6 = 11 cm
Click for solution
Dispersion Red Violet Click for solutions On entering the glass: Each colour slows down by a different amount Therefore, each colour is refracted by a different amount
Angle of incidence must be greater than the critical angle The ray must be in an optically more dense material Click for solutions
Image 4 4 Click for solutions Move the object further from the lens