Light-Emitting Diodes are Really Useful Flashcards by Verity Russell

What does LED stand for?

Light-emitting diode

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When do LEDs emit light?

When a current flows through them in a forward direction

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What are they used for?

The numbers in digital clocks, in traffic lights and in remote controls

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How are they different from a light bulb?

They don’t have a filament that can burn out

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CGP GCSE Physics (237 decks)

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Speed and Velocity are Both How Fast You’re Going

Acceleration is How Quickly Velocity is Changing

Distance-Time Graphs Tell You How Far Something has Travelled

Velocity-Time Graphs can have a Positive or Negative Gradient

Gravity is the Force of Attraction Between All Masses

Weight and Mass are Not the Same

The Very Important Formula Relating Mass, Weight and Gravity

There are Loads of Different Types of Force

You Can Draw the Forces Acting on a Body

Friction is Always There to Slow Things Down

You can Investigate the Motion of a Toy Car on a Ramp

You Could Play Around with the Experimental Set-up

First Law - Balanced Forces Means No Change in Velocity

Second Law - A Resultant Force Means Acceleration

Resultant Force = Mass x Acceleration

Resultant Force is Real Important - Especially for ‘F = ma’

The Third Law - Reaction Forces

Vectors Have Size and Direction - Scalar Quantities Only Have Size

To Work Out Resultant Force You Need to Combine Vectors

Moving Objects Can Reach a Terminal Velocity

The Terminal Velocity of Falling Objects Depends on Their Shape and Area

Hooke’s Law Says that Extension is Proportional to Force

You Can Investigate Hooke’s Law with a Spring

Hooke’s Law Stops Working when the Force is Great Enough

A Material Can Return to its Original Shape After an Elastic Deformation

Many Factors Affect Your Total Stopping Distance

Thinking Distance

Braking Distance

Momentum = Mass x Velocity

Momentum Before = Momentum After

Forces Cause Changes in Momentum

A Moment is the Turning Effect of a Force

The Centre of Gravity Hangs Directly Below the Point of Suspensión

A Question of Balance - Are the Moments Equal?

Forces are Not Always Equal Across All Supports

And if the Moments are Not Equal...

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The Properties of a Circuit

The Standard Test Circuit

Five Important Points

Mains Supply is a.c, Battery Supply is d.c

There’s a Formula Linking V and I

Four Hideously Important Current-Voltage Graphs

Light-Emitting Diodes are Really Useful

Some Components Can Change Resistance

Series Circuits - All or Nothing

Parallel Circuits - Everything is Independent

Charge Through a Circuit Depends on Current and Time

When a Charge Drops Through a Voltage it Transfers Energy

Appliances must be Earthed or Insulated

Earthing and Fuses Prevent Fires and Shocks

Circuit Breakers Have Some Advantages Over Fuses

Resistors Get Hot When an Electric Current Passes Through Them

Electrical Power and Fuse Ratings

Electrical Appliances Transfer Energy Electrically

Like Charges Repel, Opposite Charges Attract

Conductors Conduct Charges - Insulators Don’t

A Static Charge Cannot Move

As Charge Builds Up, So Does the Voltage

Investigating Static Electricity

Gold-Leaf Electroscope

Suspending a Charged Rod

Van de Graaf Generators Make Your Hair Stand on End

The Fuel-Filling Nightmare

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All Waves Have Wavelength, Frequency, Amplitude and Speed

Wave Speed = Frequency x Wavelength

Waves Can Be Transverse or Longitudinal

All Waves Transfer Energy and Information Without a Transferring Matter

Two or More Waves Moving Together Have Wavefronts

The Doppler Effect Makes Waves Longer or Shorter

There are Seven Types of Electromagnetic (EM) Waves

Radio Waves are Used Mainly for Communications

Microwaves are Used for Satellite Communication and Heating Food

Infrared Radiation is a Used for Heating and to Monitor Temperature

Light Signals Can Travel Through Optical Fibres

Visible Light is Also Useful for Photography

Ultraviolet is Used in Fluorescent Lamps

X-Rays Let Us See Inside Things

Gamma Radiation Can be Very Useful For Sterilising Medical Equipment

Gamma Radiation Can be Very Useful For Sterilising Food

Some EM Radiation Can be Harmful to People

Higher Frequency EM Radiation is Usually More Dangerous

Reflection of Light Lets Us See Things

Waves Can be Refracted

Draw A Ray Diagram for a Refracted Wave

Rays Passing Through a Glass Block are Refracted Twice

Triangular Prisms Disperse White Light

Every Transparent Material Has a Refractive Index

Find the Refractive Index of Glass a Using a Glass Block

Use Semicircular Blocks to Show Total Internal Reflection

You Can Use Snell’s Law to find Critical Angles

Optical Fibres and Prisms Use Total Internal Reflection

Sound Travels as a Wave

An Oscilloscope Can Display Sound Waves

Loudness Increases with Amplitude

The Higher the Frequency, the Higher the Pitch

Find the Period of a Wave on an Oscilloscope to get its Frequency

You Can Use an Oscilloscope to Measure the Speed of Sound

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Energy is Transferred Between Energy Stores

There is a Principle of Conservation of Energy

Most Energy Transfers Involve Some Losses, Often by Heating

You can Calculate the Efficiency of an Energy Transfer

How to Use the a Formula - Nothing to It

We Generally Can’t do Anything Useful with Wasted Energy

A Ball Rolling Up a Slope

A Bat Hitting a Ball

An Electric Kettle Boiling Water

A Battery-Powered Toy Car

A Bunsen Burner and Beaker

The Thickness of the Arrow Represents the Amount of Energy

Energy Transfer by Heating can Happen in Three Different Ways

Thermal Radiation Involves Emission of Electromagnetic Waves

Conduction - Occurs Mainly in Solids

You Can do an Experiment to Demonstrate Conduction

Convection of Heat - Liquids and Gases Only

The Immersion Heater Example

You Can See Convection Currents Using Coloured Crystals

You Can Reduce the Rate of Energy Transfer

You Can Investigate Emission of Thermal Radiation With a Leslie Cube

‘Work Done’ is Just ‘Energy Transferred’

And Another Formula to Learn

Power is the ‘Rate of Doing Work’ - I.e How Much per Second

Movement Means a Energy in an Object’s Kinetic Energy Store

Raised Objects Store a Energy in Gravitational Potential Energy Stores

Falling Objects Also Transfer Energy

Non-Renewable Energy Resources Will Run Out One Day

Most Power Stations Use Steam to Drive a Turbine

Advantages of Fossil Fuels

Disadvantages of Fossil Fuels

Nuclear Reactors are Just Fancy Boilers

Wind Farms - Lots of Wind Turbines

Geothermal Power - Heat from Underground

You Can Capture the Sun’s Energy Using Solar Cells

Solar Water Heating Panels

Cooking with Solar Power

Wave Power - Lots of Little Wave Converters

Tidal Barrages Generate Energy When the Tide Goes In and Out

Hydroelectricity - Catching Rainwater

Pumped Storage Gives Extra Supply Just When it’s Needed

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Density is Mass per Unit Volume

You Can Find the Density of an Object from its Mass and Volume

Pressure is Force per Unit Area

Pressure Differences in Liquids and Gases Depends on Density

Kinetic Theory Can Explain the Three States of Matter

Evaporation is a Special Example of Changing States

You Can Obtain a Temperature-Time Graph for Water

Absolute Zero is as Cold as Stuff Can Get - 0 Kelvins

Energy in Particles’ Kinetic Energy Stores is Proportional to Temperature

Particle Theory Says Colliding Gas Particles Create Pressure

At Constant Temperature ‘pV = Constant’

At Constant Volume ‘p/T = Constant’

Specific Heat Capacity Relates Temperature and Energy

You can Find the Specific Heat Capacity of Water

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Magnets Produce Magnetic Fields

Magnetic Field Patterns can be Seen Using Compasses

Magnetism can be Induced

A Current-Carrying Wire Creates a Magnetic Field

The Magnetic Field Around a Straight Wire

The Magnetic Field Around a Flat Circular Coil

The Magnetic Field Around a Solenoid

Magnetic Materials can be ‘Soft’ or ‘Hard’

A Current in a Magnetic Field Experiences a Force

Fleming’s Left-Hand Rule Tells You Which Way the Force Acts

4 Factors which Speed up a Simple D.C Electric Motor

Loudspeakers Work Because of the Motor Effect

Electromagnetic Induction

The Dynamo Effect - Move the Wire or the Magnet

A.C Generators - Just Turn the Coil and There’s a Current

Transformers Change the Voltage - but Only Alternating Voltages

The Transformer Equation - Use it Either Way Up

Transformers are Nearly 100% Efficient So ‘Power in = Power Out’

Transformers Make Transmitting Mains Electricity More Efficient

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At the Centre of Every Atom is a Nucleus

Isotopes are Atoms with Different Numbers of Neutrons

Radioactive Decay is a Random Process

Background Radiation is Everywhere All the Time

Nuclear Radiation Causes Ionisation

Alpha Particles are Helium Nuclei

Beta Particles are Electrons

Gamma Rays are Very a Short Wavelength EM Waves

You Can Identify the Type by its Penetrating Power

You can Investigate the Penetration of a Radiation

Balancing Nuclear Equations

The Radioactivity of a Sample Always a Decreases Over Time

Measuring the Half-Life of a Sample Using a Graph

Medical Tracers Use Beta or Gamma Radiation

Radiation is Also Used to Treat Cancer

Food and Equipment can be Sterilised Using Gamma Rays

Radiation is Used in Industry for Tracers and Thickness Gauges

Ionising Radiation Can Damage Cells and Tissues

Exposure to Radiation is called Irradiation

Contamination is Radioactive Particles Getting onto Objects

Radioactive Waste is Difficult to Dispose of Safely

Nuclear Power Stations use Nuclear Fission Chain Reactions

Nuclear Reactors Have to Work-Safely

Nuclear Fusion - Joining Small Nuclei

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We are Part of the Milky Way Galaxy

Our Solar System has One Star - The Sun

Gravity Provides the Force That Creates Orbits

The Force due to Gravity Depends on Mass and Distance

There are Different Types of Orbit

You can Calculate Orbital Speeds

Stars can be Classified by their Colours

You can Compare Brightness using Absolute Magnitude

You can See Different Types of Star on the Hertzsprung-Russell Diagara,

Waves are Affected by the Motion of the Source

Light from Galaxies is Red-shifted

Calculating Red-shift

Red-shift Suggests the Universe is Expanding

There’s Microwave Radiation from All Directions

This Evidenced Suggests the Universe Started with a Bang

The Transformer Equation - Use it Either Way Up

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Light-Emitting Diodes are Really Useful Flashcards

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