Static electricity, magnetism and electromagnetic induction (11,12,13) Flashcards Preview

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Flashcards in Static electricity, magnetism and electromagnetic induction (11,12,13) Deck (20)
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When does static electricity occur?

When electric charges (when electrons)are transferred onto or off the surface of an insulator


When do insulators become negatively charged?

when electrons move onto the insulator (polythene) from another object from friction (cloth). Because they are gaining electrons


When do insulators become positively charged?

When electrons move off the insulator (acetate) onto the cloth . Because they are losing electrons.


How does earthing happen?

When a charge is built up and then electrons are transferred back into the earth to get rid of the charge.


How do lightning strikes happen?

1) water particles (or ice) in clouds gain electrons from other particles by friction as they rub against each other
2) the cloud gains electrons and an overall negative charge
3) electrons in the ground are repelled by the cloud
5) lightning jumps as electrons to get rid of the charge


What is electrostatic induction?

for example when a negatively charged balloon touches a neutral wall, the positive charges in the wall get attracted to the balloon and they attract as the balloon has induced a charge on the wall.


What direction does the electric field point in a positive charge?



What charge does an electric field have if it is point inwards?

Negative charge


What is an induced magnet?

A magnet like an electro magnet which can be turned off


What is the name of the type of magnet which cant be turned of and is always magnetic?

Permanent magnet


What four metals are magnetic?

Steel, iron, nickel and colbalt


What is Flemings left hand rule?

Used to find either the direction of the field, direction of current or direction of the force. (usually in the context of a motor)
Force/Movement: ThuMb
Field: First Finger
Current: seCond finger


What is a solenoid?

A wire in a coil which can create a strong magnetic field when charged.


What is Flemings right hand grip rule?

Used to find either the direction of current or field around a wire
Your thumb points in the direction of the current.
Your fingers curl in fist in direction the field.


What is the motor effect?

A simple electric motor can be built using a coil of wire that is free to rotate between two opposite magnetic poles. When an electric current flows through the coil, the coil experiences a force and moves. This is called the motor effect. The force is always strongest when the wire is perpendicular to the direction of the magnetic field.


How do you calculate the force on a wire?

magnetic field strength x current x length
(magnetic flux density)


potential difference across primary coil/potential difference across secondary coil =

= number of turn in primary coil/number of turns in secondary coil

re arrange to find individual values


What are step up transformers and what are they used for?

They increase the voltage. This is used in the national grid to improve efficiency as there is less resistance. Because of the equation power = current x voltage,
If the power stays the same yet the voltage increases, the current has to decrease. When the current decreases there are less electrons and therefore less resistance.


How do step up transformers work?

On the transformer, one side, the primary coil, will have only a few coils of wire around the iron core whilst on the side, secondary coil, there are many more coils. A changing AC current is put into the primary coil which causes a changing magnetic field to be made. This then induces a voltage on the secondary coil because the magnetic field moves the electrons inside the wire creating an AC current. Because there are more coils this side, there will be an increased voltage.


What is a generator?

A generator consists of a wire coil wire that is rotated inside a magnetic field. As the coil turns, a voltage is induced in the wire.
The ends of the coil are connected to slip rings. Electrical contact with an external circuit is made using carbon brushed, which press on slip rings. A generator like this produces an alternating current