Electromagnetism

Magnetism KS2 Forces and magnets notice that some forces need contact between 2 objects, but magnetic forces can act at a distance observe how magnets attract or repel each other and attract some materials and not others compare and group together a variety of everyday materials on the basis of whether they are attracted to a magnet, and identify some magnetic materials describe magnets as having 2 poles predict whether 2 magnets will attract or repel each other, depending on which poles are facing  KS3 Forces non-contact forces: … forces between magnets… Magnetism magnetic poles, attraction and repulsion magnetic fields by plotting with compass, representation by field lines Earth’s magnetism, compass and navigation the magnetic effect of a current, electromagnets, DC motors (principles only)

Magnetism KS4 Forces forces and fields:…magnetic.. Electricity   Forces forces and fields:…magnetic.. Electricity the domestic a.c. supply; live, neutral and earth mains wires, safety measures power transfer related to p.d. and current, or current and resistance Magnetism and electromagnetism exploring the magnetic fields of permanent and induced magnets, and the Earth’s magnetic field, using a compass magnetic effects of currents, how solenoids enhance the effect how transformers are used in the national grid and the reasons for their use

Electrical induction and generation Magnetism Now that pupils understand magnets and have seen that electrical currents can make magnets it is time to show that magnetism and electricity are two parts of the same thing. A commonly seen thing in schemes of work is to have this section split up into separate sections even though they are all uses of the same thing. Electrical induction and generation Motor effect

Introducing Electromagnetism. Activity 8: Electromagnetic induction. You need a strong magnet, an analogue ammeter and a LOT of wire. Show the deflection of the ammeter with; a single wire, multiple wire loops then lots!. (Check if you have a Helmholtz coil in school)

The diagram shows a wire moving in a magnetic field The diagram shows a wire moving in a magnetic field. Your teacher will demonstrate this. A What happened when the wire was moved down quickly between the poles of the magnet? What happened when the wire was moved up quickly between the poles of the magnet? What happened when the wire was held still between the poles of the magnet? What happened when the wire was moved more slowly? What happened when the magnet was turned around? What happened when the wire was moved towards the North pole of the magnet?

2. The diagram shows bar magnet moving in a coil of wire 2. The diagram shows bar magnet moving in a coil of wire. Your teacher will demonstrate this. What happened when the magnet was pushed into the coil? What happened when the magnet was at rest inside the coil? What happened when the magnet was pulled out of the coil? 3. What do you think will happen if: the magnet is moved faster? the magnet is turned around? the magnet is pushed into the other end of the coil? two magnets, with like poles together, are pushed into the coil? Now watch the demonstration and see if you are right.

The motor effect. Activity 9: Inducing motion in a foil strip. Use a thin foil strip connected to a DC power supply. Identify the direction of the current, Force and magnetic field.

Force on a current carrying wire What happens when… … the current is turned on? … the magnetic field is reversed? To do this turn around the magnet. 3) … the current is reversed? To do this swap over the wires in the power supply. 4) … an Alternating current is used? To do this move the wires to the yellow sockets

An electric current generates a magnetic field How does the motor effect work? An electric current generates a magnetic field

Point your thumb… Point your thumb in the direction of the current… Your fingers show the direction of the field lines.

Which way is the field?

How does the motor effect work? straighten and shorten!

Mic on the right, Finger on the trigger Mic on the right, Finger on the trigger! (Fleming's gangsta-rapper rule)

Force on a current carrying wire

A coil of wire concentrates the magnetic field inside the coil

Motors Activity 10: Motors There are many simple ways to make motors. A google search will reveal many that only require a couple of paperclips, a battery, some wire and a strong magnet. Today we will be using motor kits

Motors Wind a coil of wire around the centre spindle. The coil of wire must wrap the same way (clockwise or anticlockwise) around the spindle and can not double back. You can use small bands to hold the wires in place. The ends of the wire must line up on either side of the spindle axis and be free of plastic coating or varnish. It may help to insulate the axis metal with cello tape. Mount the spindle between the two axle pins using an axle. At this point the spindle should rotate 360 degrees freely without catching

Explaining motors Applying the left hand motor rule to each side of the conductive loop will show that the induced force is in a different direction on each side causing a twisting motion.

Explaining motors The commutator allows the current direction in the loop to switch as the loop turns over, this keeps the force in the same direction.

Summarizing A SPLIT ring commutator is required for a DC motor to work as the current must be reversed in the loop. AC motors and generators have a SLIP ring commutator as the current changes direction on its own.

Summarizing An electrical current can be induced by moving a wire through a magnetic field. This principle is used in generators. Generators are usually AC due to how easy it is to transmit over long distances. A wire in a magnetic field will experience a force when a current flows through it. This principle is used in motors. Motors and generators are two kinds of ELECTROMAGNETIC MACHINE, the last kind of electromagnetic machine that pupils need to know about at GCSE/A-Level is the transformer.

Building Transformers. Activity 11: Transformers Pupils create a simple transformer to demonstrate the basic principles of its operation. Use the transformer to light an LED demonstrating the transmission of electricity without a conductive route for electricity.

Transformer construction http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/generation_transmission_electricity/transmitting_electricityrev2.shtml

Vs Ns Vp Np 10 Volts ? Volts 100 coils 100 coils

Isolation transformer Can you think of a reason why a transformer would have the same number of coils of wire on the primary and the secondary? 1000 coils 1000 coils

Transmitting electricity Explain how the transformers allow electricity to be transferred more efficiently. Explain why a very high voltage is essential to transfer electricity around the country on the National Grid.

Energy loss on the national grid. 𝑃=𝑉𝐼 𝑉=𝐼𝑅