# Physics

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• Created by: Biancaa
• Created on: 18-05-14 12:25
How to work out the gradient of a graph?
Height divided by base
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What is scalar? Give the associated graph
Only size. Distance time graph
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Wh,at is vector? Give the associated graph.
Size and direction e.g momentum. Velocity and time graph
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When does a object have zero resultant force?
When the object is at rest or if the object continues at the same speed and direction.
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What is work done?
Energy transfer= work done. OR WORK DONE=force applied x distance moved
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What is the law of conservation of momentum?
In a closed system, momentum before= after. Momentum is conserved in any collision or explosion providing no external forces act on the object.
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What does a diode do?
Allows current through in one direction
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What does a fixed resistor do in a circuit?
Limits the current
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What charge are welectrons
Negative
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Explain metals using electrons
Metals have electrons which move freely between positively charged metal ions. The material that loses electrons becomes positively charged.
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What does a variable.resistor do?
Allows current to be varied
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What does a fuse do?
Designed to melt to break the circuit if the current is too large
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What is ohms law
The current through a resistor at a constant temperature is directly proportional to the potential difference across the resistor. A filament bulb is not a oh I. Conductor because it increases in temperature as ions move ore freely
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Describe a series circuit
No choice of route so current is the same throughout. The voltage is shared between component. Adding up all The resistance= total resistance.
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Describe parallel circuit
If there a break, other parts of the circuit will still go on. Voltage is the same throughout. Bigger the resistance, smaller the current. Add current= total.
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What colour is the earth wire, live wire and neutral wire?
Green and yellow=earth, brown= live and blue= neutral
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What must be ensured when making a metal case appliance
That an earth wire must be attached. Plastic case appliances don't need one because they're double insulated with a two core cable containing a live and neutral wire. The higher the current, the thicker the cable needs to be.
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Explain fuses.
Always in series with the live wire so that it cuts off when blown. The rating should be higher than normal so that the appliance can work with the normal current.. A RCCB cuts off current quicker
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What part of a velocity time graph represents distance travelled?
The area
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What can accelerating show?
Speeding up, slowing down or changing direction
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What is a spring constant?
The force needed to stretch it.
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What is the limit of proportionality?
The extension is directly proportional to the force applied. The limit of proportionality is when too much force is applied
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What is a circuit breaker?
An electromagnetic switch that opens and cuts off the supply if the current is bigger than a certain value.
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What is an electric current?
Flow of charge
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What is a current?
Flow of electrons
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What are X-rays used for? And describe issues and how it works
To make images and CT scans, to destroy tumor at or near the surface. X-rays can damage living tissue when they pass through it. They're absorbed more by bone and teeth than by soft tissue. They can cause cancer as well as treat them.
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Describe ultrasound
Sound waves. They're partly reflected at a boundary between two different types of body tissue. It is non ionising therefore it's safer than X-rays
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What is refraction?
The change of direction of light as it passes from one transparent object into another. When waves change speed when they cross a boundary. The change in speed of the waves cause a change in direction, unless the waves are traveling across a normal.
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What is a refractive index
Measures how much the substance can refract a light ray. N=sin(I) divided by sin(r)
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What is the critical angle and total internal reflection?
The angle of incidence which maximum refraction occurs. Total internal reflection occurs when the angle of incidence of a light ray in a transparent substance is greater than the critical angle.
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What is the plumb pudding theory?
a sphere that is positively charged with negatively charged ion. And that it has no nucleus.
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What did Rutherford discover?
That particles straight back= must have a small nucleus (concentrated enough to make alpha particles bounce back). Particles changed direction= nucleus must be positively charged (repel as movement). Particles passed straight through= atom has space
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What type of radiation is the most dangerous in the body and why?
Alpha because it is easily absorbed by cells (most ionising and least penetrative)whereas beta and gamma pass right through it (less ionising, most penatrative)
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What is an isotope?
atoms with the same number of protons but different numbers of neutrons (same atomic number and different mass number)
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Where is the mass and atomic number on the periodic table?
mass= top, bottom=atomic
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What is nuclear fission?
the splitting of a nucleus into smaller fragments and releasing 2 or 3 neutrons and energy. Occurs when neutrons hit a uranium-235 nucleus or plutonium-239 nucleus- fissionable istopes
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Describe inside a nuclear reactor
fuel rods contain fissionable isotope, control rods absorb surplus neutrons to stop the chain reaction (slows down collision), water cools and slows down neutrons (fission won't occur if neutrons too fast), water also turn turbines
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What is nuclear fusion?
forcing 2 nuclei close enough together to form a single larger nucleus with a high temperature. This is difficult as they're both positive and will repel.
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What is the importance of high temperature when forcing two nucleus together?
They provide nucleus enough speed to overcome the force of repulsion between the positive nuclei so the
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Why is it difficult to maintain the conditions for achieving high heat when forcing two nucleus together
plasma containing the nuclei is heated by passing large electric currents through it. THe plasma is contained in a magnetic field so that they don't need to touch the reactor walls (touching the walls would cool it down, stopping the reaction)
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## Other cards in this set

### Card 2

#### Front

What is scalar? Give the associated graph

#### Back

Only size. Distance time graph

### Card 3

#### Front

Wh,at is vector? Give the associated graph.

### Card 4

#### Front

When does a object have zero resultant force?

### Card 5

#### Front

What is work done?