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AC & DC

Alternating Current (AC) Voltage The current changes direction 50 times every second (frequency = 50Hz) Time AC is easier to generate than DC

If the cell is reversed the current flows in the opposite direction Direct Current (DC) The current only flows in one direction Voltage Time If the cell is reversed the current flows in the opposite direction Return to menu

Generating Electricity

Generating Electricity We can generate electricity through Electromagnetic Induction……… Electromagnetic Induction: The Creation of a Voltage (and maybe a Current) in a wire which is experiencing a Change in Magnetic Field

Electromagnetic Induction The ‘field lines’ have to be cut. No current is produced if the magnet is not moving! N If You push a magnet into a coil the electrons in the coil are also given a push. This makes an ‘induced voltage’

Electromagnetic Induction Notice the needle moves in the opposite direction N If You pull a magnet out of the coil the electrons in the coil are once again given a push. This makes an ‘induced voltage’ in the opposite direction

How Can You Increase the Size of the Induced Current? Move the Magnet Faster Use a Stronger (not bigger!) Magnet Put more Turns on the Coil

Will it make AC or DC Current? We can use a magnet, coil and movement to generate electricity with this device Will it make AC or DC Current?

This is a Generator You will have heard them near road works generating the electricity to make the traffic lights and machines work

AC Generator Induced current can be increased in 4 ways: Increasing the speed of movement Increasing the magnetic field strength Increasing the number of turns on the coil Increasing the area of the coil

Bikes often have Dynamos to make electricity to light a bulb Dynamos are slightly different from generators as they rotate the magnet

If the Needle on the Centre Spot Galvanometer Moves Right 1 Division When the Magnet Is Placed Into the Coil, What Happens When…. The magnet is pulled out at equal speed? The magnet is put in faster? The magnet is left motionless inside the coil?

1) Explain what happens when the handle turns at a constant rate Use the Key Words in your answer: Magnet, coil, flux, a.c, bulb shines, movement 2) Give 3 methods to increase the brightness of the bulb Return to menu

Transformers

Transformers Transformers transform (change) the Voltage Transformers only work on AC because there is constantly changing flux

Step Up & Step Down Primary Coil Secondary Coil Primary Coil Step Up Transformer More turns on the Secondary Coil Step Down Transformer More turns on the Primary Coil

Some Transformers Look Like This….. …..you might have heard their characteristic ‘hum’

The Transformer Equation Primary voltage = Number of turns on Primary Secondary voltage Number of turns on Secondary The ratio of the turns on the coils equals the ratio of their voltages

No. of Turns on Secondary Complete the table Primary Voltage Secondary Voltage No. of Turns on Primary No. of Turns on Secondary Step Up or Step Down? 12V 36V 100 ? 600V 300V 20 20,000V 50,000V 1,000 23V 230V 150 Return to Menu