Term
| Why is the iron core laminated? |
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Definition
| To break up the currents flowing through the core, to reduce Eddy currents. If it wasnt laminated the transformer would become less efficient as heat would be lost. |
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Term
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Definition
| Eddy currents are the circular movements of the induced current.[image] |
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Term
| How does a transformer work? |
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Definition
| When the primary coil has an alternating current, this produces a changing magnetic field in the iron core. This produces a alternating potiential differnce in the secondary coil which produces an alternating current in the secondary coil. |
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Term
| Ho does a shake torch produce electricity? |
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Definition
- The torch is shaken to and fro.
- The magnet moves in and out of the coil.
- The magnetic field cuts through the coil.
- A potiential difference is induced across the ends of the coil.
- An electric current is induced in the circuit.
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Term
| Why does refraction take place? |
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Definition
| If light passes from air into a glass block. The change in density from the air to glass effects the speed the light travels. So the light bends if it is hit at an angle. |
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Term
| What happens at stage 1 of a new star being formed? |
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Definition
| A nebula is formed, hydrogen and dust particles. |
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Term
| What happens at stage 2 of a new star being formed? |
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Definition
| The nebula gathers together, becoming denser and denser under gravity. This forms a protostar. |
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Term
| What happens at stage 3 of a new star? |
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Definition
| The protostar becomes denser and hotter, so hydrogen nuclei start to fuse together to form bigger atoms such as helium. |
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Term
| Why does stage three remain stable for millions of years? |
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Definition
The outward pressure of radiation is equal to the inwards force of gravity. Its at equilibrium.
Also sufficient fuel to last that long. |
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Term
| What happens at stage 4 of a new star? |
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Definition
| Hydrogen runs out so lighter atoms such as helium fuse with other light atoms to form heavier elements such as gold. The star then expands and becomes a red giant. |
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Term
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Definition
| The enormous pressure of the collapse of a star forces smaller nuclei into eachother and they fuse together to create heavier elements such as iron and heavier. The supernova scatters them into space. |
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Term
| What happens after a star becomes a red giant? |
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Definition
- The pressure of the collapse forms a white dwarf, very dense but small in diameter.
- Bigger stars form supernovas which then become a neutron star.
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Term
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Definition
| A star denser than a white dwarf, if the neutron star is big enough it becomes a black hole. Its gravitational potiential is so great not even radiation or light can escape it. |
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Term
| What happens to the ultrasound which reaches a boundary between two different media but is not reflected? |
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Definition
| The ultrasound wave is absorbed/transmitted by the media |
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Term
| Where is the centre of mass of a hanging object? |
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Definition
| Directly below the point of suspension. |
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Term
Why is this ladder unlikely to topple?
[image] |
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Definition
| The centre of mass of the man and the ladder has a line of action which is inside the base. There is no resultant force so it is unlikely for the line of action to move outside the base. |
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Term
| What is the purpose of the slip rings and brushes on a energy generator? |
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Definition
To provide a continuous electrical connection through brushes on stationary contacts. They also avoid tangling.
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Term
| Name a light detecting device within a camera? |
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Definition
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Term
| What does a converging/convex lense look like? |
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Definition
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Term
| What does a diverging/concave lense look like? |
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Definition
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Term
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Definition
When the rays pass through eachother (they intersect) and it can be projected.
This is the kind of image inside a camera and your eye. |
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Term
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Definition
| A virtual image is an image that cannot be captured on screen. It is defined as an image in which the outgoing rays from a certain point of the object will never intersect. For instance, an image formed by the mirror is a virtual image. |
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Term
| What is centripetal force? |
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Definition
| Is the resultant force which acts towards the centre of the circle is moving in. |
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Term
| Why does the moon stay in orbit to the Earth? |
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Definition
| There is a centripetal force that is provided by gravity / gravitational attraction between the Moon and the Earth. |
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Term
| Why are there concrete blocks on cranes? |
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Definition
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Term
| What are 2 features of ultasound? |
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Definition
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It has a very high frequency /
pitch.
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Above the (upper) limit for
humans / above 20 000 Hz
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Term
| Explain how roating a coil within a magnetic can cause a connected lamp to light? |
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Definition
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The coil cuts through the magnetic field.
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A potential difference is induced
(across ends of the coil).
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The coil is part of a circuit.
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The potential difference causes a current in the circuit / lamp.
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The slip rings and brushes enable the coil to be connected
without twisting the leads / wires so the lamp lights up.
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Term
| How can something be moving at a steady speed in a circle but be accelerating at the same time? |
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Definition
Acceleration occurs when direction changes, Velocity is has a direction and
acceleration is rate of change of velocity.
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Term
| In what direction does an object accelerate moving in a circle? |
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Definition
| Towards the centre of the circle its travelling in. |
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Term
| Sound waves are caused by.... |
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Definition
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Term
| what shape do the planets orbit the sun? |
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Definition
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Term
| Why are the wires insulated in transformer coils? |
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Definition
| To prevent a short circuit through the coils and the iron core. |
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Term
| Why are step down transformers used? |
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Definition
| To reduce the voltage to a low domestic level to prevent fatal electric shocks (safer). |
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Term
| Why are step up transformers used? |
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Definition
| To increase the voltage to an efficient level, to reduce power loss. |
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Term
| What are the advantages of the National Grid? |
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Definition
- Less power stations, so less pollution.
- Electricity is available even in rural/remote areas.
- More reliable than local small power stations.
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Term
| What causes the acceleration in a circular motion of planets? |
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Definition
| gravitational force between the planet and the sun/moon/satellite. |
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Term
Ultrasound is a .......... wave.
Which ...... be heard by humans. |
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Definition
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Term
| Why might something topple over? |
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Definition
The centre of mass has been moved.
The line of action is outside the base which produces a resultant moment. |
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Term
| Why is the potiential differnce produced in a electric motor, changing? |
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Definition
| Because the changing magnetic field cuts the coil and p.d varies as the distance between magnet and coil changes / as the magnet rotates. |
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