Electromagnetism Flashcards
What is a magnetic field
area around a magnet where a magnetic material (iron, steel, cobalt and nickel) will experience a force.
How does a compass work
It points in the direction of Earth’s magnetic field
How to show magnetic field lines around a bar magnet
Place a bar magnet on a sheet of paper. Sprinkle iron filings onto the sheet around the magnet. The filings will line up with the field lines showing its pattern.
Place a bar magnet on a sheet of paper. Place a plotting compass on the paper and mark the ends of the needle. Move the compass to one of the points and repeat the process until you have a loop going from one pole of the magnet to the other. Join the lines with a ruler. Repeat in different places on the sheet until you have a field diagram.
How is a magnetic field induced in a wire
When a current flows through a conducting wire a magnetic field is produced around the wire. The field lines are circular.
Magnetic field of a solenoid
The magnetic field inside a solenoid is strong and uniform. It has a similar shape to that of a bar magnet.
How to make solenoid stronger
Add an iron core - it is now an electromagnet.
Motor effect
When a conductor carrying a current is placed in a magnetic field the magnet producing the field and the conductor exert a force on each other.
How does a motor rotate
A coil of wire in a magnetic field carries current in two opposite directions. One side of a coil experiences a force in one direction and the other side experiences the other. With an axle through the centre of the coil it will rotate.
Generator effect
If an electrical conductor moves relative to a magnetic field (cutting through the field lines) or if there is a change in the magnetic field around a conductor, a potential difference is induced across the ends of the conductor. If the conductor is part of a complete circuit, a current is induced in the conductor.
Difference between altenator and dynamo
A dynamo uses a split-ring commutator to reset the current each half turn of the coil, allowing the induced current to remain in one direction (D.C.).
An alternator uses complete ring commutators to maintain a constant connection with the output circuit so that the induced current is going in the opposite direction after each half turn of the coil (A.C.).
Why are transformers important
Step-up transformers increase potential difference whilst reducing the current for a given power. This makes transmission more efficient as less energy is wasted through resistive heating.
