physics topic 12 - mangetism and the motor effect!

like magnets…

repel

unlike magnets….

attract

describe the uses of permanent and temporary magnetic materials including cobalt steel iron and nikel?

steel = permenant ( fridge door )

iorn = temporary ( door bells,cranes and speakers)

what is a permenant magnet ?

the magnet produces it’s own magnetic field permenantly

what is a temporary/induced magnet?

only produce a magnetic field when they are in another magnetic field

describe the shape and direction of the magnetic field around the bar magnet and and for a uniform field?

where the lines are most concentrated that’s where magnetic field is the strongest

further away = weaker magnetic force

what is a uniform field?

lines are the same distance apart meaning strength is the same everywhere?

describe the use of plotting compasess to show the shape and direction of the field of a magnet and the earth;s magnetic field?

1. Place the magnet on the piece of paper and draw around it 

2. Place the compass near the edge of the magnet ( needle will align itself in the direction of the field line )

3. Move the compass so that it points away from the new dot, and repeat the process above

4. Repeat this and join up the marks you made ( you will end up with a drawing of one field line around the magnet

5. repeat until you get various field lines

How do we know the earth’s core is magnetic?

geographic north pole is acc magnetic south pole #

a magnetic compass points north proving the earth has a magnetic field

what is the right hand rule?

When a current flows through a long straight wire a magnetic field is created around it

reversing current also reverse the direction of the field

what is a solenoid?

coil of wire

in the middle the field lines are uniform very close magnetic field are strong

On the outside of the solenoid the overlapping field lines cancel each other out and produce weaker field lines

what is the motor effect?

how to increase the field strength of a solenoid?

increase the size of the current

add an iotn cotr which becomes an induced magnet

increase the number wire loops

how do loud speakers work?

coil is wrapped around a permenant magnet so the a.c signal cuaes a force on the coil which moves the cone

when current is reversed the force acts in an oopsite direction these movements make the cone virbate which creates a sound wave

Explain how an insulator can be charged by friction, through the transfer of electrons

when the materials are charged together they become electrically charged
the electrons transfer from one material to another
the rod looses electrons

The material gaining electrons= negatively
charged
The material losing electrons becomes equally
positively charged

e is - c so the rod becomes +
clothes gaines e therefore left with an = - e

why do we feel an electric shock?

electirc charge builds up on an object ( p.d between object and earth increases )
+ p.d large e- jumps acrosss the gap between the object and the earth ( spark )

jump any earth conductor near by

why does lightning occur?

• Clouds can build up an electrostatic charge. • When this charge becomes large enough, the clouds discharge via the air to the earth. • This is known as lightning

why does a charged baloon stick to the wall?

- Rubbing a balloon on a wool jumper gives the balloon a negative charge by transferring electrons.
- This leaves the jumper with a positive charge.
- The wall is neutral at first.
- When the balloon gets close to the wall, it pulls the positive charges in the wall to the surface.
- The balloon sticks to the wall because opposite charges attract!

what is an electric field?

an electric charge will experience a force

how is static electricity used in electrostatic sprayers?

1) spray gun charged up with small droplets of paint
paint drop replls all others bc they have same charge
2)object being paiten given oposite charge attracts the spray of apaint
3) method gives even coating ( no paint is waisted )

dangers os static electricity in refullling cars?

as fuel flows into the pipe can build up charge of static can build up cause explosion

dangers of static on areoplane?

as plane fly reiction between air and plane causes charge
interfere with communication equipment