P7 - Magnetism Flashcards
What are naturally magnetic materials called?
Permanent
Which 3 metals are already magnetic?
Iron, nickel and colbolt
Where is the magnetic field strongest?
At one of the poles
The arrows go out of the South Pole and into the North Pole. True or false?
False. On a magnetic field diagram, the arrows showing attraction go out of the North Pole and into the South Pole
Describe a solenoid and what it does
Wire coiled around an iron core, and this creates an elecromagnet
Complete the sentence:
The more coils there is in a solenoid, the…
stronger the magnetic field
Fill the blanks:
Any wire with ___________ running through has a ________ _____ going _______________ around it
Electricity
Magnetic field
Perpendicularly
Complete the sentence:
The less current or the thinner the wire, the…
weaker the magnetic field
What creates the magnetic field in an electromagnet?
The electrons travelling rapidly in the wire
If the current is going down, the direction of the magnetic field is going…
Clockwise
To figure out which direction the magnetic field is going around a wire, which is best to do it?
Righty tighty, lefty loosey - When the current goes up, you want to loosen the ‘screw’, so it would go left around the wire/ screw - anticlockwise
If you create an electromagnet with a steel core, will it still work when it is turned off?
Yes, steel is the longest lasting permanent magnet. Iron stops as soon as the electricity stops running though it
According to Flemming’s Left Hand Rule, label the three fingers
Thumb - Force
1st Finger - Magnetic Field
2nd Finger - Current
How do you calculate the force from a magnetic field (N)?
magnetic field strength x current x length of wire
T) ([symbol B]) x (Amps) x (m
How does a compass work?
Inside the compass is a tiny bar magnet. The north pole of this magnet will attract to the south pole and vice versa. The arrows point in the direction of the magnetic field
The Earth has poles. What does this say about the Earth’s core?
It is magnetic
What is an induced magnet?
Magnetic materials that turn into a magnet when they’re put through a magnetic field
What type of force is always between the permanent and induced magnets?
Attractive
What happens when you take away the magnetic field from an induced magnet?
It quickly loses its magnetism/ most of it. It will stop producing a magnetic field
A moving charge creates what?
A magnetic field (solenoids). When current flows through a wire, a magnetic field is created around the wire
Around a wire, what is the magnetic field made of?
Concentrated circles perpendicular to the wire with the wire in the centre
When the current changes direction…
The magnetic field does too.
To find the direction, put up your right thumb, and the thumb is the current, the fingers curled up are the magnetic field
The larger the current in a wire, the weaker the magnetic field is.
The closer to the wire, the stronger the magnetic field is.
True or false?
False:
The larger the current in a wire, the stringer the magnetic field is.
The closer to the wire, the stronger the magnetic field is
Which of these make the strength of a solenoid stronger?
a) With/ without an iron core
b) More/ less coils
c) Thicker/ thinner wire
d) More/ less current
a) With an iron core - this is an electromagnet
b) More coils
c) Thicker wire
d) More current
What is the motor effect?
When a current- carrying wire (or any other conductor) is put between 2 attracting magnetic poles, the magnetic field around the wire interacts with the magnetic field it has been placed in.
This causes the magnet and the conductor to exert a force on each other. This causes the wire to move
How can the full force of the motor effect be seen?
When the wire is at a 90 degree angle to the magnetic field. If the wire runs parallel to the magnetic field, it won’t experience any force at all.
The force always acts at right angles to the magnetic field of the magnets and the direction of the current in the wire
Also, an increase in the current will increase the force
Give the formula to find the size of the force acting on a conductor in a magnetic field. What is the limitation of this formula?
Force = Magnetic flux density x Current x Length N = T/ tesla x Amps x metres
It must be at 90 degrees to the magnetic field it is in
What is a split ring communicator?
It swaps the contacts every half turn, so the wires don’t get tangled, and the motor will keep rotating in the same direction
How can you increase the speed of a motor?
Increasing the current, adding more turns to the coil, or increasing the magnetic flux density
How can you see the magnetic field of a magnet?
Using a compass around it, and tracing the lines the needle points in - into South, out of North
Which way do the lines on a magnetic field go to?
into South, out of North.
Why on Earth - on the surface of the magnet - compasses point North, because they are pointing up and out of North
What will these magnetic poles do when put together?
a) North - north
b) North - south
c) South - South
d) South - north
a) Repel
b) Attract
c) Repel
d) Attract
What 2 types of magnets are there? What s the difference?
Permanent magnets - produce their own magnetic field
Induced magnets - turn into a magnet (usually temporarily) when they’re put into a magnetic field. When taken out of the magnetic field, they loose their own magnetic field (or most of it) quickly
A moving charge will create what?
Creates a magnetic field
What are the magnetic field lines around a wire carrying a current like?
Concentric circles, perpendicular to the wire. With the wire in the centre
What is the right hand thumb rule relevant for?
If you point your right thumb in the direction a wire is going in, then the magnetic field lines follow the way your fingers curl
What does the strength of a magnetic field produced around a wire depend on?
The current (the larger the current, the stronger the field is) The distance from the wire (the closer to the wire, the stronger the field is)
What is a solenoid?
A coil of wire - this produces a magnetic field
What can be used to increase the strength of a solenoid?
By having an iron core inside the coiled wire
What makes a solenoid with an iron core an electromagnet?
1) It is created with a wire carrying current
2) When you turn off the current, the magnetic field disappears
Fill the blanks:
The magnetic field inside a solenoid is ______ and _______ (same strength and direction at every point in that region).
Outside the coil, the magnetic field is just like a ___ ______.
This means that the ends of a solenoid act like the north and south _____ of a ___ ______
Strong Uniform Bar magnet Poles Bar magnet
How can you increase the field strength of a solenoid?
Putting a block of iron in the centre of the coil Increasing the amount of coils Increasing the voltage Decreasing the resistance Switch from AC to DC
When will the motor effect occur?
When you put a current carrying wire in a magnetic field - useful in electric motors
Explain the motor effect, when a current carrying wire is put between magnetic poles
The magnetic field around the wire interacts with the magnetic field it has been placed in. This causes the magnet and the conductor to exert a force on each other, and can cause the wire to move
What changes can be made for the wire to feel the full force of the motor effect?
The wire must be 90 degrees to the magnetic field
If the wire runs parallel to the magnetic field, then it won’t experience any force at all
The magnitude (strength) of the force increases with
The strength of the magnetic field (motor effect)
Also, with the amount of current passing through the conductor
What is the equation to find the size of the force in teh motor effect?
F = BIL
Force = Magnetic flux density x Current x Length
(N/ Newtons) = (T/ Tesla) x (A/ Amperes) x (m/ metres)
- only when the current is at 90 degrees to teh magnetic field it is in, the force acting on it can be found with this equation
What is the magnetic flux density?
How many field (flux) lines there are in a region. This shows the strength of the magnetic field
Measured in T or Tesla, symbol is B
B = F/ il (force/ (current x length)
What do the 3 fingers in Fleming’s left hand rule stand for?
Thumb - Force (the way the wire will move)
First finger - (magnetic) Field (north to south, point to south)
Second finger - Current (after drawing current arrows, from positive to negative)
What does Fleming’s left hand rule show will happen if the current is reversed?
The direction of the force will be reversed
What does Fleming’s left hand rule show will happen if the magnetic field is reversed?
The direction of the force will also be reversed
Which way do you draw current arrows?
From positive to negative
Which way do you point the magnetism finger for Fleming’s left hand rule?
North to south - point to south
