9J - Force Fields and Electromagnets Flashcards
What is an electric field?
The space around a charged object where a charged particle experiences a force.
What is the direction of an electric field?
From positive to negative
What is the direction of a magnetic field line, outside a magnet?
From North pole to South pole
What happens to a negatively charged object in an electric field?
It moves in the opposite direction to the field lines.
What shape is the electric field close to a current-carrying wire?
It is circular going around the wire and the direction can be found using the right-hand grip rule.
An object close to a current-carrying wire is unaffected when the current direction is reversed. This means the object must have…
No charge
What is the order of events for static electricity that can be produced in some materials?
Rubbing brings the surfaces of two materials into close contact over a large area. Temporary bonds form between the atoms on the surfaces of the two materials. Electrons pass from one material to the other. If two dissimilar materials are being used, the material that attracts electrons the most strongly ends up with more electrons than it had originally.
What is a bar magnet?
It is a magnet with 2 ends, a North pole and a South pole. They repel and attract other poles.
What has a gravitational field?
Any object with mass
What is the equation for weight?
Weight (N) = Mass (Kg) x Gravitational field strength [g] (N/Kg)
What is weight
The gravitational force of attraction that Earth uses attract masses to its centre
What happens when you lift an object above the ground
Gravitational potential energy is stored in the mass of the object. The higher it is, or the greater the maths, the more energy it stores.
What causes static electricity?
A charge can build up when two different materials rub together.
What does static electricity cause?
Shocks or sparks. Sparks can accidentally start fires.
What happens when two different insulating materials are rubbed together?
Some electrons are transferred.
Why can’t protons be transferred?
Because they are fixed in the nucleus of the atom
What happens when you rub a conducting material?
The electrons spread out in the metal so we don’t notice a charge.
What does an object charged with static electricity attract?
Uncharged objects (but the force isn’t strong)
Two charged charged objects with the same charge…
Repel each other
Two charged charged objects with the opposite charge…
Attract each other
What is an electric current?
The flow of electrons
Series circuit:
- The current is the same everywhere in the circuit
- All the bulbs go off if one is broken
- If you add more bulbs, the current is reduced
Parallel circuit:
- The current is split when it comes to a junction
- Each bulb is controlled individually
- If you add more bulbs, the current stays the same
What do ammeters measure?
Amps - The current
What do voltmeters measure?
Volts - Voltage
What is voltage?
The pressure of the electrons moving through the current
What is resistance?
How easy or difficult it is for the current to flow.
What causes a high resistance?
- A long wire
- A thin wire
- Insulating materials
What causes low resistance?
- A short wire
- A thick wire
What metals are the best conductors?
Copper, silver, gold and aluminium
How to calculate resistance?
Voltage = Current x Resistance
How to calculate voltage?
Voltage = Current x Resistance
Resistance graphs
- Current = y-axis
- Voltage = x-axis
- Highest resistance = top line
How do you increase the strength of an electromagnet?
- Increasing the number of coils
- Increasing the current
- Using a magnetic material as a ‘core’ inside the coil of wire
Any wire has …
an magnetic field around it
What happens when the wire is wrapped in a coil?
It forms a magnetic field similar to a bar magnet (electromagnet)
What is a relay?
It improves safety by using a small current to turn on a big current. It means people don’t have to touch the big current.
What is the motor effect?
If a wire (which has a magnetic field) is in the magnetic field of a bar magnet. The two fields affect each other and experience a force
What is an electric motor?
A coil of wire in a magnetic field. When the current flows through the wire, the combo of the two magnetic fields cause the coil to spin
