AVERAGE SPEED. When calculating the AVERAGE SPEED of an object you need to know the DISTANCE travelled by the object and the TIME taken to travel that distance. You then use the following equation:. average speed = distance. time. V = d. Where v – average speed (m/s)
When calculating the AVERAGE SPEED of an object you need to know the DISTANCE travelled by the object and the TIME taken to travel that distance. You then use the following equation:
average speed = distance
V = d
Where v – average speed (m/s)
d - distance (m)
t - time (s)
L.I: To calculate the average speed of a trolley on a slope
APPARATUS: slope, trolley, timer,meter stick
METHOD: measure distance on slope
release trolley and start timer together
stop timer when trolley reaches 2m mark.
To calculate the speed of sound experimentally.
fast timer,2 microphones,metre stick
Place the 2 microphones 1m apart. Switch on timer. Clap hands above start microphone. Record time in table. Repeat twice more. Calculate average time using v = d/t.
Speed of sound equals 340m/s.
The speed of light is much faster than the speed of sound. Think of a thunder storm. You see the lightning then you hear the thunder. This is because the light reaches us almost immediately.
The values we need to know are:
Speed of sound = 340m/s
Speed of light = 300000000m/s
The equation we use is:
Distance = speed x time
d = v t
In 1836, Samuel Morse demonstrated the ability of a telegraph system to transmit information over wires. The information was sent as a series of electrical signals. Short signals are referred to as dits (represented as dots). Long signals are referred to as dahs (represented as dashes). With the advent of radio communications, an international version of Morse code became widely used.
The most common method of communicating with wires is the telephone. The TRANSMITTER (mouthpiece) contains a MICROPHONE which changes sound energy to electrical energy. The RECEIVER(ear piece) contains a loudspeaker that changes electrical energy into sound energy.
Sound signals are transmitted down wire at almost 300000000 m/s (speed of light) and the signals can be displayed using an oscilloscope as shown:
Messages can be sent from one place to another by using waves. They are sent from a transmitter to a receiver. You will have heard of radio, tv and microwaves.
A typical wave pattern is shown below:
To calculate the speed of a wave we use the equation:
V = f x
Where v = velocity (m/s)
f = frequency (Hz)
= wavelength (m)
The number of complete waves that pass a point every second. Symbol f, units – hertz (hz).
The distance from a point on a wave to the next similar point – from crest to crest. Symbol (lambda), units - metres (m).
The distance a wave travels each second. Symbol v, units – metres per second (m/s)
The maximum height of the wave above or below the zero line. Units – metres (m).
Old fashioned receiver
Radio signals are waves that transfer energy. They are sent from a transmitter at a speed of 300000000m/s and picked up by a receiver. Wires are not needed between the transmitter and the receiver.
Modulator: combines the 2 electrical signals
Amplifier: makes the combined signal bigger
Aerial: changes electrical signal into a radio wave and sends them in all directions.
Aerial: Picks up all radio waves.
Tuner: Selects the frequency you want.
Decoder: Separates the radio wave from the sound wave.
Amplifier: Makes the weak signal stronger.
Power supply: Needed for amplifier.
Loudspeaker: Changes electrical signal to sound.
Aerial: Picks up all wave energy.
Tuner: Selects the TV frequency you want.
Decoder: Selects the sound signal Decoder: Selects the picture from wave. signal from wave.
Amplifier: Makes the sound signal Amplifier: Makes the picture stronger. signal stronger
Loudspeaker: Changes electrical TV Tube: Changes electrical signal to sound. signal to light
High frequency signal
High frequency signal
Modulator: combines high frequency signals with audio and video signals.
Amplifier: electrical signals are made stronger.
Aerial: signals are changed to TV and radio waves.
A tv picture is built up by a series of lines. An electron beam scans across the television tube (electromagnetic deflection). A special coating gives out light when the beam passes over it. The beam starts at the top then scans backwards and forwards till it reaches the bottom. There are 625 lines for one picture and 25 pictures per second.
In a colour tv there are three electron guns. There are three colours of light given out by the fluorescent paint on screen. These are red, green and blue. All colours can be made by mixing these three :-
yellow - red & green
magenta - red & blue
cyan - green & blue
white - red, blue & green
Amplitude modulation is a way of varying the amplitude of a high frequency radio wave so that it carries a low frequency audio wave
Low frequency audio wave
Amplitude modulated wave
Waves with a long wavelength can bend round or over obstacles much better than short wavelengths.
Radio waves have a longer wavelength than TV waves. This is why in some hilly regions you can receive good radio reception but not a good tv picture.
To investigate the relationship between the angle of incidence and the angle of reflection for a plane mirror.
Power supply, ray box, mirror, single-slit and a protractor.
The angle of reflection is equal to the angle of incidence.
LEARNING To find out about TOTAL INTERNAL INTENTION: REFLECTION.
APPARATUS: Ray box, single slit, semi-circular block & protractor
METHOD: Set up apparatus as shown.
Send a single beam along 20o line. Draw path of ray. Repeat for an angle of 60o
CONCLUSION: When no light passes from the perspex to the air, we have TOTAL INTERNALREFLECTION taking place
How curved reflectors make signals stronger