Physics Unit 3B flashcards

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What is a moment?
The turning effect of a force.
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What is the equation for moments?
moment = force x perpendicular distance from the line of action to pivot.
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What is the advantage of having a large spanner?
The force can exert a larger movement because the distance from the pivot is greater.
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What angle must you push at to get the maximum moment / turning effect?
a right angle.
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What is the centre of mass?
The point at which the whole mass is concentrated.
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What happens when the anticlockwise moments are equal to the clockwise moments?
The object wont turn.
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Why do levers act as force multipliers?
Because they reduce the amount of force needed to get the same moment by increasing the distance.
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Give 2 examples of levers.
Wheel barrows and scissors.
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What happens if the moments acting on an object arent equal?
The object will turn as there will be a RESULTANT MOMENT.
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Why are low and wide objects most stable?
Because there is less chance of their line of action or weight being outside the base of the object, causing a resultant moment.
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What is the time taken for a pendulum to swing from one side to the other and back called?
time period
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How is time period calculated?
Time period = 1(seconds)/frequency (hz)
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Why are liquids incompressible?
Because you can't squash them, their volume and density stay the same, therefore a force applied to one point will be transmitted to other points in the liquid.
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Where is pressure transmitted in a liquid?
Equally in all directions.
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What is pressure? What is the equation for pressure?
Force per Unit Area. pressure = force/cross-sectional area.
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What are Hydraulic Systems?
Force multipliers-they use a small force to produce a bigger force. They do this by using liquid and cross-sectional areas.
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How do Hydraulic Systems work?
The system has 2 pistons, one with smaller area. The first piston has force exerted on the liquid with a small force over a small area. This force is transmitted to the 2nd piston. The 2nd piston has a larger area so there is a larger force.
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Give examples of where hydraulics are used?
Car brakes, car jacks, manufacturing and deployment of landing gear on some aircraft.
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What is the equation for force?
force = pressure x area
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What is velocity?
The speed and direction of an object
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How does circular motion occur?
If an object is travelling in a circle its constantly changing direction and velocity. This means the object is accelerating towards the centre of the circle. There must be a resultant force acting on the object for the acceleration to occur.
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What is the force that keeps something moving in a circle called?
Centripetal force.
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What does centripetal force depend on?
Mass, speed and radius. The higher the mass and the faster the speed, the bigger the centripetal. You need a larger force to keep something moving in a smaller circle as it has more turning to do.
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What is a magnetic field?
A region where magnetic materials (like iron and steel) and also wires carrying currents experience a force acting on them.
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What happens when a current flows through a wire?
A magnetic field is created around he wire which is made up of CONCENTRIC CIRCLES with the wire in the centre.
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What is the magnetic field inside a coil of wire (a solenoid) like?
Strong and uniform.
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How do you increase the strength of a magnetic field around a solenoid?
Adding a metalically soft iron core. This turns it into an electromagnet.
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Why are electromagnets useful?
Because they can be magnetised and demagnetised quickly and easily.
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What is the motor effect?
A force experienced by a current-carrying wire in a magnetic field.
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What factors speed up an electric motor?
More current or a stronger magnetic field.
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What is a split-ring commutator responsible for in an electric motor?
Swapping the contacts every half turn to keep the motor rotating in the same direction.
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How is the direction of a motor changed?
By changing the polarity of the DC supply or swapping the magnetic poles over.
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How does a motor work in a fan/CD player/ hairdryer etc?
By linking the coil to an axel, so the axel spins round, then attach the fan etc to it.
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What is electromagnetic induction?
The creation of a potential difference (voltage) across a conductor which is experiencing a change in magnetic field.
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What induces voltage?
Moving a magnet in a coil wire. If you keep the magnet moving backwards and forwards you produce a potential different that swaps current, an AC supply.
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How do generators work?
By turning a magnet half a turn, which means that then the direction of the magnetic field through the coil reverses. This constant changing creates an AC.
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What do step-up transformers do?
Step the voltage up by having more coils on the secondary coil. Greater potential difference on secondary coil.
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What do step-down transformers do?
Step down the voltage by having more coils on the primary coil. Less potential difference on secondary coil.
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How do transformers work?
The primary coil produces a magnetic field within the iron core so most of it is passed to the secondary coil. The rapidly changing magnetic field is felt by the secondary coil. The changing field induces an alternating p.d across the secondary coil.
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What does the iron core of an electromagnet carry?
Magnetic field (not current)
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What is the transformer equation?
p.d across primary coil/p.d across secondary coil = no. of turns on primary/no. of turns on secondary (power in = power out, as they are 100% efficient almost.)
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What are switch mode transformers?
A type of transformer that operates at higher frequencies between 50KHz and 200 kHz. The higher frequencies means they can be made lighter for use in mobile phone chargers. They use little power when they're switched on but with no load.
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Other cards in this set

Card 2

Front

What is the equation for moments?

Back

moment = force x perpendicular distance from the line of action to pivot.

Card 3

Front

What is the advantage of having a large spanner?

Back

Preview of the front of card 3

Card 4

Front

What angle must you push at to get the maximum moment / turning effect?

Back

Preview of the front of card 4

Card 5

Front

What is the centre of mass?

Back

Preview of the front of card 5
View more cards

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