physics test

how do dynamos on a bike wheel work + disadvantages

• the core gains a magnetic field which changes due to the alternating current

• these magnetic field lines are then cut by the wire, which induces a voltage across the coil causing a current

• this turns the light on

• the brightness of the light is dependent on how hard the person pedals

how to plot a magnetic field experiment

• draw around a bar magnet

• take a compass and place at the end of a bar magnet, draw a dot where the arrow points

• replace compass and repeat until line is formed

• repeat other side of magnet

• draw 3 other field lines

describe how a hydroelectric power station works

• water inlet → GPE transferred to the kinetic energy store of the water mechanically to turn a turbine

• fossil fuels can be used to heat water and produce steam to turn turbines

• energy from the chemical store of the fuel transfers to the kinetic store of the turbine to the kinetic store of the generator, then electrically to the national grid

how to use left hand rule

• thumb is for thrust

• second finger for field

• middle finger for current

how does the coil move in a motor

• when current flows through the coil of wire, it produces a magnetic field, which interacts with the other magnetic field, producing a force

• this force causes movement

• the split ring commutator alternates the current every half turn, making it continuously spin

• the brushes maintain contact with the communtator allowing continous current to flow

feature of wind farms

• renewable

• produces no pollution or CO2

• cheap to build and maintain

• not reliable - wind

• some people consider them visual pollution

features of hydroelectric power station

• renewable

• can respond to meet changes in demand

• no pollution or CO2 produces (unless pump is used to return the water as this uses fossil fuels)

how does a loudspeaker produce sound waves

• loudspeakers have a coil attached to a cone in a magnetic field

• when ac flows through the coil, the core is continuously pushes forward/back, making a sound

• the frequency and pitch of the sound can be altered by changing the frequency of the ac used