Magnectic Fields Flashcards
(27 cards)
What tells you how strong a magnet is?
The distance between the magnetic field lines
What direction do the magnetic field lines travel around a magnet bar?
From north to south around the magnet
Look in book for diagram
How does the right hand grip rule work?
The thumb Indicates current and the direction of fingers indicates direction of the current
How does the right hand grip rule apply for a solenoid?
Fingers indicate the direction of current flow and your thumb will always point to the North Pole.
Look in Book for diagrams to explain when the coil is going over the wire or behind it.
Why must the wire used be insulated?
To prevent any short circuits
How can the strength of a magnetic field be increased?
- By using a larger current
- By increasing the number of coils around the solenoid
What effect does replacing the iron core of a solenoid with a wooden one?
It would weaken the magnetic field as it doesn’t have free electrons to carry a charge
What do magnetic field lines look at between two magnets?
Look in book
Straight lines from North to south equal spaces apart
Explain Fleming’s left hand rule?
Look in book
The thumb shows the direction of the force
The first finger shows the direction of the magnetic field
The second finger shows the direction of conventional current
What happens with Flemings left hand rule if the magnetic fields and current are parallel?
No force acts in any direction
What would happen to the direction of force on a wire if an alternating current is used?
The direction of current alternates clockwise and anticlockwise which would change the direction of the force back and forth.
What is electromagnetic induction?
Whenever a wire cuts the lines of a magnetic field an electromotive force is induced
How do you increase the EMF?
- Move the wire faster
- Use a stronger magnet
- Use a coil of wire and increase the tones
Describe what is observed on the centre-zero ammeter when the magnet is moved slowly in a metal coil?
When the south pole of the magnet is moved slowly towards the coli a south pole is created on the coil at the side facing the magnet, opposing motion.
Creating a small deflection to the left.
Describe what is observed on the centre-zero ammeter when the magnet is moved quickly out of a metal coil?
When the south pole of the magnet is moved quickly away from the coil a north pole is created on the coil at the side facing the magnet, opposing motion.
Creating a large deflection to the right.
Describe what is observed on the centre-zero ammeter when the magnet is stationary in a metal coil?
The ammeter stays at zero with no deflection either way as no magnetic field line are cut.
What is a transformer?
Used to reduce or increase the voltage or amps of a current.
Using a primary circuit with a number of turns and secondary circuit with a number of turns connected by a soft iron core which the current runs through with 99 percent efficiency.
What is a summary of using DC for a transformer?
1: Push the switch down
2: Hold the switch down
3: Release the switch down
What kind of current do generators use?
A.C
Why is transformer used?
To transfer energy across the grid in the most efficient manner possible.
By increasing the current to reduce energy lost as heat.
How is a step-down transformer used?
- The primary voltage is stepped down in the secondary which
has less number of turns N. - By stepping down the voltage, the current is increased.
- The voltage is now suitable for use, such as 240 V in homes.
How is a step-up transformer used?
The primary voltage is stepped up in the secondary
which has a greater number of turns N.
By stepping up the voltage, the current is reduced.
This reduces power losses in the cables, as P = I2 R
What values is the voltage stepped up to onto the power grid?
- 400,000 V
- 275,000 V
- 132,000 V
What value of voltage is used in homes?
240
