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. What would you like to do?
speed = ?
speed = distance/time
What is acceleration?
Acceleration is the change in speed of an object.
What is the formula for acceleration?
- a = (a - u) / t
- = (finishing speed - starting speed) / time
How can you identify a constant speed in a Distance-Time Graph?
The vector is represented in a straight line.
How do you know a speed of an object is increasing on a Distance-Time Graph?
The line is curved and headed up.
What does deceleration look like on a Distance-Time Graph?
- A bent line which gradually becomes more and more horizontal.
How can you show a constant speed on a Velocity-Time Graph?
With a straight, horizontal line.
What does acceleration look like on a Velocity-Time Graph?
- A straight, inclined line.
What does a constant deceleration look like on a Velocity- Time Graph?
- A straight line inclined downwards.
How do you work out the distance travelled from a Velocity-Time Graph?
You work out the area under the line representing the speed. This is the distance travelled.
What are the four fundamental forces in nature?
Gravitational force, Friction, Elastic force and Electrostatic.
Why does gravitational force exist?
Objects have mass, thus they attract each other.
What is electrostatic force responsible for?
It is responsible for binding everything together.
Where can we find elastic force?
When an object is stretched or compressed.
What is friction?
Friction is a force that opposes motion. Without it, objects would keep on moving without stoping (as if they were in space).
What is Newton's first law?
An object travels at a constant velocity unless it is acted on by an un balanced force.
What is Newton's second law?
- F = ma
- The larger the mass of an object the greater force will be need to accelerate the object.
What is the difference between mass and weight?
The difference between mass and weight is that mass is the force that resist other forces and makes things up and weight is the mass x gravity.
What happens to an object as it falls?
It is pulled down by a constant force, g. As the object falls faster the air resistance upon that object grows, forcing the object into terminal velocity.
What is terminal velocity?
Terminal velocity is when a falling objects reaches a constant speed and stops accelerating.
What principles mainly effect stopping distances of cars?
- Ice and snow
- Mass of the vehicle
- Speed of the vehicle
What is a moment?
It is when a force acts at an angle and makes a turning effect.
What is the equation for a moment?
moment = force x distance of force from pivot
What does Hooke's law state?
The extension of a material is in direct proportion to the load that is applied.
Describe the sections of this graph regarding Hooke's law.
- A = This is the section that obeys Hooke's law
- B = Limit of proportionality
- C = Elastic Limit
- D = Yield Point (permanent deformation)
- E = Breaking Point
How far away is the moon from the Earth?
Values of g for:
Pluto (not a planet)
- Mercury 4.0 g
- Venus 8.9 g
- Mars 3.7 g
- Pluto 0.6 g
- the Moon 1.6 g
- Jupiter 24.8 g
What is known as perihelion and aphelion?
In an elliptical orbit, a planet is in its perihelion when it is closest to the son and is in its aphelion when it the farthest.
What shape are the orbits of comets?
- Very elliptical
What force cause objects to orbit others?
How do you calculate the orbital speed of a satellite?
- orbital speed = (2pi x orbital radius) / time
- Take into account that the orbital radius is measure from the centre of the object.
What is the radius of the Earth?
Name all the planets in order from closest from the sun
What are galaxies formed from?
Solar systems (stars)
What is the nearest star?
How long is one light year?
94600000000000 km (11 0's)
What is the universe made up of?
The universe is made up of collections of billions of galaxies.
What are 4 different electrical hazards?
Frayed cables - one touching it may be shocked and there is also the risk of fire
Long cables - The longer the cable the more heat is produced ( can be offset by using thicker cables)
Damaged Plugs - touching the metal conductors
Water - conducts electricity (kitchen, bathroom)
What are 5 ways to make electricity safe?
Insulation - by covering the cables, sockets, metal conductors with plastic
- Double insulation -
Earthing - A 3rd wire, through which no electricty flows, is connected to the metall casing and to a metal plate buride underground. If either of the first two wires become lose and touch the metal case, the electricity is led to the underground metal plate avoiding anyone from getting electrocuted.
- Fuses - these protect wires. When wire overheat, fuses shut them down in order to prevent an accident.
- 3 amp (for up to 700 watts) and 13 amp (for over 700 watts)
Circuit breakers - fuses that can be reset. They detect when the earth wire is used.
What is a Watt?
Wattage is the amount of electricity consumed per second.
1 watt = 1 joule/second
What is the formula for calculating electrical power?
- Power = current x voltage
- P = IV
- I is in amps (A)
- V is in volt (V)
With what formula can you calculate how much electrical energy is being used?
What are AC and DC?
- Alternating Current and Direct Current.
- DC is the sort of current from a battery. It will from continuously - to + ends.
- AC is the current from a socket. The direction of the current changes all the time.
What device can be used to compare the direction of AC and DC?
When do you know you need to use AC instead of DC and vice-versa?
What are the two mains types of circuits?
- Series circuit and Parallel circuit.
- In the series circuit, electrons only have one route to the + end, whereas in a parallel there are more routes.
How can you measure the current in a circuit?
With an ammeter.
What are and how do LDR's work?
Light- Dependent Resistors moniter light levels and as light becomes stronger, the LDR becomes more resistant, allowing less electricity to flow.
What are Thermistors?
These change their resistance according to the temperature. The can either decrease or increaser in resistance, depending on the thermistor itself.
What is and how do LEDs work?
A light-emitting diodes devices that light up as a current passes through them.
In which direction do electron flow?
Towards the positive end of the power source.
What formula can we use in order to relate charge, current and time?
- Current = charge transferred / time taken
- I = Q/t
- Q - charge measure in coulombs (C)
- I - current measured in amps (A)
- t - time in seconds (s)
What is Ohm's law?
- V = IR
- V - voltage in Volts (V)
- I - current in amps (A)
- R - resistance in ohms (Ω)
Name some insulator and conductors?
- Conductors = Silver, Copper, Gold, Aluminium
- Iron, Brass, Bronze, Mercury
- Graphite, Dirty Water, Concrete
- Insulator = Glass, Rubber, Oil, Asphalt,
- Porcelain, Cotton, Wood, Plastic,
- Diamond, Pure Water
What are the two types of waves?
Transverse and Longitudinal
What are transverse waves?
The particles of the substance move up and down at right angles.
What are longitudinal waves?
- These waves move back and forward.
- An example would be sound waves.
What are these features of waves?
What is the meaning of the amplitude in a wave?
It is the amount of energy in a wave.
What is the frequency of a wave?
- It is the number of waves which pass through a point within one second.
- It is measured in hertz (Hz)
- 1 Hz = 1 wave per second
What is the formula for the frequency and period of a wave?
- Period = 1 / frequency
- T = 1/F
What equation do all wave follow?
- The Wave Equation
- v = f λ
- v - speed in metres per second
- f - Hz
- λ - wavelength in metres
What is light?
- Light is a vibration in the electric and magnetic fields that surround us.
- It is an electromagnetic wave which enables us to see.
- It is a part of the electromagnetic spectrum.
What part of the electromagnetic spectrum is visible?
Wavelengths between 700 nm and 400 nm.
What do all frequencies in the EM spectrum have in common?
- Their wave speed in empty space.
- 300,000,000 ms(-1)
- or 3 x 10(8)ms(-1)
What are main uses of the EM spectrum?
- Radio - Communication
- Microwaves - Cooking, mobile phones
- Infrared - Heaters, night vision
- Ultraviolet - Fluorescent lamps, tanning booths
- X-rays - Medical
- Gamma - Sterilising, cancer treatment
What the main dangers of the EM Spectrum?
- Radio waves - none
- Microwaves - internal heating
- Infrared - burns skin
- Visible light - damage to vision
- Ultraviolet - skin cancer, blindness
- X-rays - mutations in skin cells, severe burns
- Gamma rays - cancers and cell mutation
What protective measures can we use against microwaves?
A small metal grid is enough.
What protective measures can we use against infra-red light?
How can you protect yourself from visible light?
- Naturally, the iris relaxes to let less light through, or tightens to allow more light to pass (in a dark enclosure).
- Wearing sunglasses.
What can you do to protect yourself from ultraviolet light?
You can use polaroid sunglasses and covering our bodies with sunblock or light clothes.
How can you to protect yourself from x-rays?
To properly protect yourself from x-ray you must stand behing a lead shield.
What can you do to protect yourself form gamma rays?
For this, you will need massive shielding from thick sheets of lead and concrete.
How can you work out the angle of a reflected ray?
- The angle of the reflected ray is the same as the incident ray.
- angles of incidence = angle of reflection
What is it called when the direction of light is changed?
How do you work out the refractive index?
sin (incident angle) / sin refracted angles = n
n - refractive index
What is the critical angle?
This is the angle at which total internal internal reflection is achieved.
sin c = 1 / n
What are the most common uses of total internal reflection?
Periscopes and transmitting information.
What type of wave is light?
What type of wave are sound waves?
What is the range of human hearing?
20 Hz - 20,000 Hz
How do you measure the speed of sound in air?
- There are two main methods.
- With the first you need 3 things:
- 50M tape measure
- Stop watch
- Outdoor wall which make an echo.
With the second method you use an electronic timer, metal block, hammer and a microphone.
In what ways can heat energy be transferred ?
What happens to the energy used for a light bulb that isn't transferred into light?
- It is emitted as heat energy.
- Energy cannot be created or destroyed.
What are 5 different types of energy?
What is the efficiency formula?
- efficiency =
- useful energy output / total energy input
How can heat energy be conducted?
Through solids (metals are the most conductive).
How can heat energy be convected?
Through gasses and liquids.
How can heat radiation be radiated?
Through electromagnetic waves, though it converts to convection when it touches a solid surface.
What are three ways homes can be insulated?
Loft insulation - thick blankets of material (fibreglass), covering any surface you intend on keeping warm. Air trapped in the fibreglass makes a very effective insulator.
Cavity wall insulation - foam is pumped into the wall and dries with air bubbles trapped in it.
Double Glazing - two sheets of glass with a layer of air in between (window).
How do we insulate our own bodies?
Fibre filled clothing and multiple layers.
What is the equation for energy or work done?
- work done = Force x distance moved
- N*m = J
What is the equation for potential energy?
PE = mgh
- PE - joules
- m - kg
- g - 10 (on Earth)
- h - metres
What is the formula for kinetic energy?
KE = 1/2 mv(2)
How do you calculate power?
P = WD / t
P - watts or kilowatts
Can you name 7 ways of generating electricity?
- Solar cells
- Fossil fuels
- Nuclear power
What different methods for generating electricity from the use of water?
- Pump storage
What is the formula for density?
Density = mass / volume
What is the formula for pressure?
- P = F / A
- P - Pascals (Pa)
- F - N
- A - area in m(2)
What is the formula for P at depth?
P = density x g x depth
What is absolute zero temperature?
- It is the temperature at which gas molecules can't move any slower.
- - 273 degrees C or 0 K
How do you convert from Celsius to Kelvin and vice versa?
- C to K - add 273
- K to C - subtract 273
What are magnetic field lines?
These are invisible lines which show the pattern of a magnetic field.
What poles are facing each other?
A north and south pole
What poles are facing each other?
- 2 south poles
- 2 north poles
How can you produce a magnetic field?
With an electric current in a conductor.
What happens to a current carrying conductor in a magnetic field?
A force is exerted on it.
What is the left hand motor rule?
- It is a rule that aid you in finding the direction of F, Magnetic field and Electrons.
- Thumb - Thrust
- Forefinger - Field
- Centre finger - Current
How can we use electromotive force?
In loudspeakers and electric motors.
When is electro magnetic voltage induced?
When the conductor is moved in a direction that is not parallel to the magnetic field lines.
What factors influence the size of the voltage induced by moving a conductor through a magnetic field?
- Speed of the movement
- Strength of the magnetic field
- Number of coils on the solenoid
What are electric generators made of and how do they work?
- They consist of two main components:
- A coil and a permanent or electro magnet.
- A rotating magnet is placed inside a coil (or vice versa) and rotates to make DC.
What are alpha, beta and gamma?
They are different ionising radiations emitted from unstable nuclei.
How can you detect ionising radiation?
Using a Geiger-Muller tube or photographic film.
What are isotopes?
Isotopes are atoms with the same atomic number but have different masses (i.e. different number of neutrons)
What are alpha rays composed of and are their penetrating power?
- Alpha rays are composed of Helium atoms.
- (2 protons + 2 neutrons)
- It can only penetrate a few cm of air, a sheet of paper is enough.
What are beta rays composed of and what is their penetrating power?
- Beta is composed of only fast moving electrons.
- It can be stopped by a few mm of metal.
What are gamma rays composed of and what is their penetrating power?
- Gamma rays are composed of high frequency electromagnetic waves. (NO MASS or CHARGE)
- You need a few cm of lead or several metres of concrete to stop it.
Why are ionising rays called so?
Because they ionise any atoms they penetrate.
How do we know when an unstable nuclei will decay?
We can't. Radioactivity is a random event.
How does a Geiger-Muller tube exactly work?
What is the half-life of an element?
It is the amount of time it takes for any unstable matter to half its activity.
What is a becqerel (Bq) ?
A becqerel a unit of measurement for activity and is equal to one piece of radiation detected per second.
What are common uses of radioactivity?
Tracers, which are radioactive elements whose pathway can be traced, are used in the study of plants and living beings and the medical field.
Radiotherapy can be used to treat cancer.
Sterilisation of medical instrument and food using electromagnetic energy.
Radiation is important for the manufacturing industry.
What are the tree protective measures against radioactivity?
What is fission?
Fission is when an unstable isotope is hit by a neutron and its nucleus splits and produces two smaller nuclei and more neutrons, starting the process again. CHAIN REACTION.
What are the three types of chain reactions?
Less than one neutron per fission - ceases
One neutron per fission - controlled chain reaction (indefinitely)
More than one neutron per fission - uncontrolled reaction, escalates into an EXPLOSION
What is a nuclear reactor made of?
- Fuel - uranium 235 that fissions easily
- Moderator - slows down neutron for better reactions
- Control rods - material which absorbs neutrons
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