P2b

physics exam 2 second part

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Static Electricity

Build up of Static Electricity is caused by Friction

Electrons are scraped of material when rubbed and dumped on another ONLY elecrtons move

The rate of flow of electric charge is called electric current

Like Repel Unlike Attract

The GREATER the charge the GREATER potential difference. When PD is big enough a spark is caused

Smoke Precipitators, Photocopiers

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Circuits

Current = flow of electrons , will only flow through a component is there is voltage across it

Voltage = Driving force that pushes current around

Resistance = anything which slows the flow down

INCREASE voltage, INCREASE current

INCREASE resistance, DECREASE current

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Resistance

Current through a resistor is proportional to voltage

Temperature in a filament increases the resistance increases

Current only flows through a diode in one direction

Potential Difference = Resistance x Current

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Symbols

Variable resistor - resistance can be changed

Diode - Makes current flow in one direction

LDR - Bright light resistance falls,

Thermistor - Hot conditions resistance falls

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Series & Parallel Circuits

Series

Potential Difference is shared, Current is the same. Resistance adds up, cell voltages add up

Parallel

Potential Difference is the same, Current is shared, Resistance, less than that of the lowest branch

Example - christmas lights so they dont all blow

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Mains Electricity

Mains is AC

Batteries are DC

UK - 230v and 50 Hz

AC is shown on an Oscillioscope

DC is a straight line on and Oscillioscope

Space between top points = time period

Frequency = 1/ Time Period

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Plugs

Metal parts made of copper or brass

Case is made of rubber or plastic

Neutral = Blue

Live = Brown

Earth Wire = green/yellow

Total Charge = Current x Time

Energy Transformed = Charge x Potential Difference

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Fuses and Earthing

Live Wire = alternating

Neutral Wire = 0v

Fuses - current is too big it blows some can be reset

Earthing - wire attached to metal casing so if somehow that gets charged then it will bring the force back. Fuse will then blow to stop it.

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Atomic Structure

Democritis - matter is made up of atomos

Dalton - different types of atoms

Thomson - Electrons can be removed (plum pudding)

Rutherford - mass in centre (nucleus) empyt space (electrons

Proton = mass 1 charge +1

Neutron = mass 1 charge 0

Electron = mass 1/2000 charge -1

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Radioactive Decay

Alpha particles = helium nuclei, big, heavy, slow. dont pentrate, stongly ionising

Beta particles = electrons, moderate, moderate, moderate etc (neutron turns to proton)

Gamma rays = short em waves, small, light, fast, good penetrating, badly ionising (too much energy)

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Background radiation

natural - air, food, rocks, cosmic rays

Humans - nuclear explosions (not much)

Level depends on: altitude, rock type, underground

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Fission and Fusion

Fission

This process involves atoms splitting, it usually uses Uranium or Plutonium, its a chain reaction.

  1. the nucleus splits into two smaller nuclei, which are radioactive
  2. two or three more neutrons and energy are released

Fusion

The joining of smaller atoms to make a bigger one.

Happens in the Sun - Hydrogen -> Helium

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