09 Electromagnetism- 4th Form Flashcards
Describe the shape of the magnetic field around a wire
Circular field shape
field lines getting futher apart- field getting weaker as you move away from the wire
How do you determine the direction of a magnetic field around a wire?
Use the right hand grip rule
Thumb- direction of current
Fingers- wrap in direction of magnetic field (clock wise or anti-clockwise)
How would you construct a simple electromagnet?
1) wrap a wire around an iron nail
2) connect a cell across the wire
What can be done to increase the magnetic field around a solenoid?
1- more turns
2- increase the current
3- add an iron core
Draw the shape of a magnetic field around a coil.
Draw the magnetic field around a solenoid.
What happens to the magnetic field around a wire if more wires are added side by side- How can you tell from the image that the magnetic field is stronger?
More wire- stronger field
The closer the magnetic field lines the stronger the field.
iron filing will line up more easily and more closely together in a stronger magnetic field.
If a vertical wire has the current upward in the wire, work out the direction of the magnetic field using your Right Hand Grip Rule
Thumb- up and in direction of current
Finger wrap in direction of magnetic field.
How would you demonstrate the direction of the magnetic field around a single wire?
Place compasses around the wire
The compass will point in the direction of the magnetic field
What happens to the direction of the magnetic field around a magnet if the direction of the current it reversed?
The direction of the magnetic field is reversed.
How do we use dot and crosses to represent the direction of a mangetic field or current?
dot means out of the page
cross means into the page
How do you use the right hand grip rule to work out which end of a solenoid is the north end?
Fingers- wrap your fingers in the direction of the current
Thumb- will point to the North end of the solenoid
What happens to the magnetic field around a solenoid if you add an iron core (magnetically soft)
Stronger magnetic field
Why is iron a better core to use in an electromagnet than steel?
Iron is magnetically soft- the domains in iron line up easily - it can magnetise and demagentise easily
Steel is magnetically hard- the domains do not line up easily- it cannot magnetise easily and it can be used to make permananet magnets becaouse it also does not easily demagnetise
Electromagets are used in electric bells.
- When the button is pushed, a current flows in the electromagnet -This creates a magnetic field around the electromagnet
- The electromagnet attracts the soft iron armature which moves to the right
- This causes the hammer to hit the bell.
What happens next?
The moment the iron armature moves to the right this creates a _break in the circuit- t_he circuit is no longer complete.
The current drops to zero and the magnetic field around the electromagnet disappears.
The iron armature is no longer attracted and springs back to the left
The armature completes the circuit again and the whole cycle repeats alowing the bell to repeatedly sound.
