# Shared Flashcard Set

## Details

Physic Unit 3
N/A
39
Physics
05/26/2011

Term
 Why is the iron core laminated?
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.
Term
 What are Eddy Currents?
Definition
 Eddy currents are the circular movements of the induced current.[image]
Term
 How does a transformer work?
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.
Term
 Ho does a shake torch produce electricity?
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.
Term
 Why does refraction take place?
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.
Term
 What happens at stage 1 of a new star being formed?
Definition
 A nebula is formed, hydrogen and dust particles.
Term
 What happens at stage 2 of a new star being formed?
Definition
 The nebula gathers together, becoming denser and denser under gravity. This forms a protostar.
Term
 What happens at stage 3 of a new star?
Definition
 The protostar becomes denser and hotter, so hydrogen nuclei start to fuse together to form bigger atoms such as helium.
Term
 Why does stage three remain stable for millions of years?
Definition
 The outward pressure of radiation is equal to the inwards force of gravity. Its at equilibrium. Also sufficient fuel to last that long.
Term
 What happens at stage 4 of a new star?
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.
Term
 How is iron produced?
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.
Term
 What happens after a star becomes a red giant?
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.
Term
 What is a neutron star?
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.
Term
 What happens to the ultrasound which reaches a boundary between two different media but is not reflected?
Definition
 The ultrasound wave is absorbed/transmitted by the media
Term
 Where is the centre of mass of a hanging object?
Definition
 Directly below the point of suspension.
Term
 Why is this ladder unlikely to topple?  [image]
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.
Term
 What is the purpose of the slip rings and brushes on a energy generator?
Definition
 To provide a continuous electrical connection through brushes on stationary contacts. They also avoid tangling.
Term
 Name a light detecting device within a camera?
Definition
 Photographic film.
Term
 What does a converging/convex lense look like?
Definition
 [image]
Term
 What does a diverging/concave lense look like?
Definition
 [image]
Term
 What is a real image?
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.
Term
 What is a virtual image?
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.
Term
 What is centripetal force?
Definition
 Is the resultant force which acts towards the centre of the circle is moving in.
Term
 Why does the moon stay in orbit to the Earth?
Definition
 There is a centripetal force that is provided by gravity / gravitational attraction between the Moon and the Earth.
Term
 Why are there concrete blocks on cranes?
Definition
 So that the crane remains stable. So that the (total) clockwise moment equals the (total) anticlockwise moment. so that the crane remains in equilibrium/balanced.
Term
 What are 2 features of ultasound?
Definition
 It has a very high frequency / pitch. Above the (upper) limit for humans / above 20 000 Hz
Term
 Explain how roating a coil within a magnetic can cause a connected lamp to light?
Definition
 The coil cuts through the magnetic field. A potential difference is induced (across ends of the coil). The coil is part of a circuit. The potential difference causes a current in the circuit / lamp. The slip rings and brushes enable the coil to be connected   without twisting the leads / wires so the lamp lights up.
Term
 How can something be moving at a steady speed in a circle but be accelerating at the same time?
Definition
 Acceleration occurs when direction changes, Velocity is has a direction and acceleration is rate of change of velocity.
Term
 In what direction does an object accelerate moving in a circle?
Definition
 Towards the centre of the circle its travelling in.
Term
 Sound waves are caused by....
Definition
 Vibrations of particles.
Term
 what shape do the planets orbit the sun?
Definition
 ellipse
Term
 Why are the wires insulated in transformer coils?
Definition
 To prevent a short circuit through the coils and the iron core.
Term
 Why are step down transformers used?
Definition
 To reduce the voltage to a low domestic level to prevent fatal electric shocks (safer).
Term
 Why are step up transformers used?
Definition
 To increase the voltage to an efficient level, to reduce power loss.
Term
 What are the advantages of the National Grid?
Definition
 Less power stations, so less pollution. Electricity is available even in rural/remote areas. More reliable than local small power stations.
Term
 What causes the acceleration in a circular motion of planets?
Definition
 gravitational force between the planet and the sun/moon/satellite.
Term
 Ultrasound is a .......... wave. Which ...... be heard by humans.
Definition
 sound can't
Term
 Why might something topple over?
Definition
 The centre of mass has been moved. The line of action is outside the base which produces a resultant moment.
Term
 Why is the potiential differnce produced in a electric motor, changing?
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.
Supporting users have an ad free experience!