Magnetism and Electromagnetism Flashcards
What are the ends of a magnet called?
Poles
How many poles does a magnet have, and what are they called?
Magnets have two poles: a north pole and a south pole.
State the law of magnetism.
Like poles (S and S or N and N) repel each other, and unlike poles (S and N) attract each other.
Define magnetically soft and hard materials.
Soft materials (e.g., iron) are easily magnetized and lose magnetism easily.
Hard materials (e.g., steel) are difficult to magnetize and retain magnetism.
What is a magnetic field line?
A magnetic field line is the region around a magnet where a force acts on another magnet or on a magnetic material.
How can permanent magnets be used to produce a uniform magnetic field pattern?
Two bar magnets with opposite poles facing each other create a uniform magnetic field in the gaps between the poles.
What produces a magnetic field around a conductor with an electric current?
When a current flows through a conducting wire, a magnetic field is produced around the wire.
Describe the construction of electromagnets.
Electromagnets consist of a coil of current-carrying wire wrapped around a magnetically soft core and can be turned on and off.
Explain the force on a charged particle moving in a magnetic field
The charged particle’s movement, creating a current, produces a force perpendicular to the direction of motion and the magnetic field.
How does a simple DC electric motor work?
A coil of wire, positioned in a uniform magnetic field, rotates when a current flows through it, producing a force due to the interaction of magnetic fields.
How does the left-hand rule predict the force direction on a current-carrying wire in a magnetic field?
The force direction is determined by the left-hand rule, where the current, magnetic field and force are mutually perpendicular:
- the thumb points towards the direction of the force experienced by the conductor
- the forefinger points toward the direction of the magnetic field
- the middle finger points toward the direction of the electric current
What factors affect the force on a current-carrying conductor in a magnetic field?
- The force increases with the magnitude of the current or the size of the magnet.
- Changing the current direction or reversing the poles changes the force direction.
What induces a voltage in a conductor, and what factors affect its size?
- Relative movement between a conductor and a magnetic field induces a voltage.
Factors affecting size:
- speed, number of turns, size of coils, and magnetic field strength.
How is electricity generated by rotating a magnet within a coil?
- Rotating a magnet or a coil in a magnetic field induces a voltage and current in the coil.
Voltage can be increased by:
- increasing wire length
- using a stronger magnet
- increasing rotation speed.
Describe the structure and working of a transformer
A transformer consists of:
- primary and secondary coils
- an iron core
- and changes the size of an alternating voltage by having different turns on the input and output sides.
Explain the use of step-up and step-down transformers in electrical energy transmission.
Step-up transformers increase voltage for transmission, while step-down transformers lower voltage for local use.
What affects the size of the induced potential difference in a transformer?
- The speed of movement
- number of turns on coils
- size of coils
- strength of the magnetic field
What is the relationship between input and output voltages for a transformer?
Input (primary) voltage / Output (secondary) voltage = Primary turns / Secondary turns.
What is induced magnetism, and how does it occur?
- Induced magnetism occurs when a magnetic material is placed in a magnetic field
- temporarily turning it into a magnet
- with one end becoming a North Pole and the other end becoming a South Pole.
Explain what happens to the metal rod AB. (4)
- Current on the rod
- Producing a magnetic field around the rod
- Magnetic fields interact
- producing a force on the rod
Describe how the alternating current generates a sound wave. (4)
- Alternating current changes direction continuously
- Current in the coil produces alternating magnetic field
- Producing force on the coil
- Reversing the direction of current reverses the direction of the force, hence coil vibrates.
Describe two ways that the student can make the pointer move to the right
- Reverse the magnet
- Move the magnet out of the coil
Apart from changing the speed of the friction wheel, suggest how the output voltage of the dynamo can be increased.
- More turns on the coil
Suggest why the current-carrying wire used in this investigation must be thick
Thin wire would melt
