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GCSE Physics > P3 Forces And Electromagnetism > Flashcards

P3 Forces And Electromagnetism Flashcards

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0
Q

What is the formula to calculate a moment?

A

Moment(newton meters) = force(N) X perpendicular distance from the line of action of the force to the pivot (m)

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1
Q

What is a moment?

A

The turning effect of a force.

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2
Q

Why do you get the maximin turning effect when the force is at right angles?

A

Any other angle will mean a shorter perpendicular distance to the pivot.

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3
Q

How does one find the centre of mass of a flat object?

A

Suspend the shape and a plumb line from the same point.
Draw a line along the plumb line on the object.
Do the same thing again but suspend the shape from a different point.
The centre of mass is where the two lines meet.

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4
Q

What causes an object to fall over?

A

It happens when the centre of mass moves beyond the edge of the bass. This will create a moment and the object will turn into the ground.

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5
Q

What can be done to increase the stability of an object?

A

Add more mass at the bottom.

Produce a wider bass.

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6
Q

Define time period.

A

The time taken for a pendulum to swing from one side to the other and back again.

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7
Q

Give the formula that calculates the time period of a pendulum.

A

Time period(seconds) = 1/frequency of the pendulum(hertz)

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8
Q

What is the relationship between pendulum length and the time period?

A

The longer the pendulum, the longer the time period.

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9
Q

What happens to pressure in a liquid?

A

Pressure in a liquid is transmitted equally in all directions.

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10
Q

What remains constant in all hydraulic systems?

A

Pressure. The force may change.

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11
Q

Define velocity

A

Speed with direction.

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12
Q

When an object is travelling in a circle, what is it doing?

A

As the direction is constantly changing, the velocity is as well. It is accelerating towards the centre of the circle.

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13
Q

What is centripetal force?

A

It is the resultant force that acts on an object, causing it to keep moving in a circle as it is pulling towards the centre.

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14
Q

What can provide centripetal force ?

A

Tension. If you swing around a weight on a piece of string, the tension of the string pulls the weight towards your hand.
Friction. If a car is going around a bend, friction between the road and the tyres make is go inwards.
Gravity. When the moon goes around the Earth, gravity pulls it towards the centre.

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15
Q

What affects centripetal force?

A

The faster the speed, the bigger the force has to be.
The larger the mass, the bigger the force has to be.
The larger the radius, the smaller the force has to be.

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16
Q

Define magnetic field.

A

A magnetic field is a region where magnetic materials (like iron and steel) and also wires carrying currents experience a force acting on them.

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17
Q

What is the direction of magnetic field lines?

A

North to south.

18
Q

When a current flows through a wire, what is created?

A

A magnetic field around the wire.

19
Q

What is a magnetically soft material?

A

They magnetise and demagnetise very easily. When the current is turned off the magnetic field disappears.

20
Q

What is the motor effect?

A

The force experienced by a current-carrying wire in magnetic field.

21
Q

What can increase the force exerted by the motor effect?

A

A greater current or magnetic field.

22
Q

When the wire carrying the current, runs parallel to the magnetic field, what happens?

A

It will feel no force. Maximum force is felt when it is at 90 degrees to the magnetic field.

23
Q

What is Flemings left hand rule?

A

The thumb is motion, the first finger field and second finger, current.

24
Q

What is the split ring commutator on an electric motor?

A

It swaps the direction of current on every half turn of the motor. This allows the motor to keep turning in the same direction constantly.
It does this by swapping the contacts every half turn.
This is only needed with a DC current.

25
Q

What is electromagnetic induction?

A

The creation of potential difference across a conductor which is experiencing a change in magnetic field.

26
Q

How does an electricity generator work? What type of current is produced and why?

A

A magnetic is turned within a coil of wire.
As the magnetic is tuned, the magnetic field through the coil changes. This produces potential difference.
When the magnetic has been half turned, the magnetic field reverses, reversing the PD. If the magnetic is kept turning in the same direction an AC current will be produced.

27
Q

How does a step up transformer work?

A

They step the voltage up. They have more turns on the secondary coil.

28
Q

How does a step down transformer work?

A

They step down the voltage by having more turns on the primary coil.

29
Q

How do all transformers work?

A

There will be an iron core. This will be like a cube of iron but with a square hole in the middle. Wire will be wrapped around two opposite sides of the iron core and current sent through one set of wire. Current will be produced on the other side as well.

30
Q

What does the iron core in a transformer do?

A

It only transfers the changing magnetic field from the primary coil to the secondary. No electricity flows around the iron core.

31
Q

Explain electromagnetic induction in a transformer.

A

The primary coil produces a magnetic field which stays within the core and gets passed to the secondary coil.
As there is an AC current, the filed in the iron core is constantly changing direction.
This change is felt by the secondary coil.
The changing field induces an alternating potential difference across the secondary coil. This is electromagnetic induction of a PD.

32
Q

What would happen if a DC current is put through a transformer and why?

A

Nothing in the secondary coil would happen. The magnetic field wouldn’t be changing so there would be no induction in the secondary coil.

33
Q

If you see an equation with an I in it, what does it mean?

A

Current.

34
Q

What makes switch mode transformers different from normal ones?

A

They operate at a higher frequency. Between 50 kHz and 200 kHz.

35
Q

What are the advantages of switch mode transformers?

A

They work at higher frequencies so can be made lighter and smaller. This is good in things like mobile phone chargers.
They also more efficient.
They use very little power when plugged in at the mains but aren’t connected to a device.

36
Q

How is an electromagnet made?

A

An insulated coil of wire with current flowing through it is wrapped around a ferro-magnet core.

37
Q

How is the strength of an electromagnet increased?

A

Increasing the voltage, wrapping the coil around more, having a core that conducts electricity more.

39
Q

What does more coils in a transformer mean to the voltage ?

A

More coils means more voltage. For example double the number of coils, double the voltage.

40
Q

What does more coils in a transformer mean to the current ?

A

The more coils, the less current. For example double the coils and halve the current.

41
Q

Why within a electric motor, would any side move?

A

The current paging through it is perpendicular to the magnetic field and it will have a magnetic field of its own. These two fields will interact and a force will be produced.

42
Q

What is the unit for frequency?

A

Hertz

43
Q

Why, in a transformer, does a AC current in the primary coil produce a AC current in the secondary coil?

A

The AC current produced an alternating magnetic field.
This travels through the core.
This creates PD, thus a current is produced.

44
Q

What is the centre of mass?

A

Where the mass of an object can thought to be concentrated.

GCSE Physics (6 decks)

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