Electromagnetic induction

When magnet field lines are broken, current flows in the conductor. (2 ways to cut)(Magnet with acoil breaking the fields induces current.)

Electromagnetic inductionCurrent must flow so as to make thenear end of coil same as pole of magnet. Use righthand grip rule with thumb pointing to the north, then fingers show direction of current.

Lenz’s Law

The direction of the induced current is always

such as to oppose the change producing it.

Electromagnetic induction

Which direction must the current flow in to make the near end south?

Electromagnetic induction

Which direction must the current flow in to make the near endnorth?

Direction of induced current

Fleming’s right hand rule

Fleming’s right hand rule

Used to determine direction of current flow in the conductor

a.c. generator

End of generators for now……

Starting the transformer principle

Mutual induction

transformer

If an alternating current is on the primary coil, this sets

up an alternating magnetic flux in the coil and thisinduces an alternating

e.m.f. in the secondary coil.Mutual inductance used in

this way is called a transformer.

Step up, step down

Step upLargerOutput e.m.f.

Step downSmallerOutput e.m.f.

Turns ratio

Secondary e.m.f = no. of turns in secondaryPrimary e.m.f. no. of turns in primary

P = VI P = I2R

Power equations

Practical transformers…reducing energy losses

• Low resistance copper coils reduces internal energy losses

• Laminated core to reduce Eddy’s current.

• Soft iron core reduce energy required to bring about magnetic reversals.

• Efficient core design the link all the primary flux with the secondary coil.