Paper 3 Flashcards
What causes pressure in gases?
Particles in the gas colliding with a surface cause a force and so a pressure
Why does atmospheric pressure change with height above the earths surface?
As height increases there are fewer air molecules above that point so the weight of air particles, which contributes to atmospheric pressure, is smaller. Atmosphere is also less dense.
What caution must be taken when using submersion?
No water may leave the beaker, so be careful to avoid splashing/spilling.
How could you increase the magnetic effect at the ends of a solenoid?
- Increase the current
- Increase coils, while keeping solenoid same length
- Decrease the length of the solenoid while keeping the number of turns the same
- Add an iron core inside the solenoid
How could you increase the magnetic field strength around a current-carrying wire?
Increase the current
Why does twisting a current-carrying wire into a solenoid lead to the magnetic effect inside the solenoid being stronger?
magnetic fields from each turn of wire point in the same direction in the centre of a solenoid
magnetic fields from each turn of wire add together.
What can you use to show there is a magnetic field around a straight, current carrying wire?
A compass
Why do compasses point north?
The earths core generates a magnetic field, and the needles of the compasses line up with it.
Describe the magnetic field that is created between the north and south poles of two bar magnets when they are placed near each other.
A uniform magnetic field is created, which means the field is the same strength and acts in the same direction everywhere between the poles. The field lines point from north to south.
Why might a current carrying wire move when placed between magnetic poles?
The magnetic field around the wire interacts with the magnetic field between the poles. The result is a force in experienced by the wire that can cause the wire to move.
Which type of current must be supplied to a loudspeaker in order for it to work?
Alternating current
Explain how a split ring commutator keeps an electric motor rotating in the same direction.
Was the contacts every half turn, so the left hand and right hand arms of the coil always experience a force in the same direction.
A loudspeaker contains a coil of wire in a magnetic field. Explain how the loudspeaker creates sound waves when an alternating current is supplied to it.
When a current is supplied to the coil, the coil feels a force that moves it in one direction. When the current flows in the opposite direction, the coil will experience a force in the opposite direction.
As a.c. is being supplied to the coil, the direction of the current, and therefore the direction of the force, keeps changing. This makes the coil move back and forth. The coil is attached to a cone, so the cone vibrates, creating sound waves.
What is meant by the term electromagnetic induction?
When a potential difference is induced across a conductor when it experiences a change in an external magnetic field.
Describe how a potential difference in a wire can be induced using a magnetic field.
Move the wire relative to the magnet, or change the magnetic field the wire is in.
