Flashcards in 2 Deck (134):
What are good conductors of electricity?
Why are metals good conductors of electricity?
Electrons can easily flow through metals
What are good insulators?
Why are plastic and glass good conductors?
Electrons cannot move through them
What materials does static electricity work with?
Why would a child's hair stand up after going down a plastic slide?
Electrons move from the child onto the plastic when he sides down -child now has positive charge
The hair is positive so hairs repel each other and stand on end
How would a someone reduce the static electricity on their body?
Touch a metal object and electrons will move onto them to neutralise the charge
What is a cell?
What is a battery in a circuit?
What happens if you close a switch on a series circuit?
The cell pushes out electrons as it turns on
Electrons travel around the circuit
What is the flow of electrons called In a circuit?
What do the electrons do?
Carry energy to appliances in the circuit
What is a series circuit?
No branches so electrons have to go in one direction
What happens if the switch is opened?
Electrons cannot flow so the current stops
Electrons no longer give appliances energy so appliances stop working
Why is the unit of current
How do we measure current
With an ammeter
What does the ammeter do?
Counts the number of electrons passing through every second to be able to work out the current
What happens to current in a series circuit ?
It is never used up
Current is the same throughout the circuit
What do parallel circuits have that series don't?
What happens to current in a parallel circuit?
The current splits at the branches and then rejoins to equal the full current
How does a light bulb light up in a circuit?
Electrons leaving cell carry energy
They give energy to bulb
Return back to cell with no energy
What is potential difference?
Energy that a cell gives to the current
What does potential difference tell us about appliances?
How much energy is used by the components
How do we measure potential difference?
What does the voltmeter measure?
The energy the electrons are carrying when they leave the cell
How much energy electrons are giving to components
What happens to potential difference in a series circuit?
Potential difference is the same throughout the circuit
Why are bulbs dimmer when there are 2 in series circuit ?
Potential difference is split
Why can one bulb be dimmer?
One bulb receives more energy
What is the potential difference in a parallel circuit?
Each branch equals the same potential difference as the cell
What happens if 2 cells point in opposite directions?
Potential difference cancels out
What happens if you have multiple cells in the same direction?
The potential difference adds up
What does resistance tell us?
Idea of the energy needed to move a current though a component
What is the unit of resistance?
How do you calculate resistance ?
What are resistors designed for?
To have a resistance so electrons need a lot of energy to pass through them
How would you make a bulb dimmer with a resistor?
Adding a resistor uses up some of the energy so the bulb is dimmer
What happens to the current through a resistor when we increase potential difference?
The current moving through a resistor is directly proportional to the potential difference across the resistor
BUT only if the temperature is kept constant
What does a filament do in a bulb?
Tightly coiled wire gets extremely hot as an electric current passes through causing it to glow and pass out light
What happens when you change the potential difference of a filament bulb and measure the current ? Why?
Current through filament bulb is not directly proportional to potential difference because the bulb gets hot which causes resistance to increase
High temps cause atoms in filaments to vibrate more so electrons in current now collide more with atoms wasting energy
What is special about a diode?
Only lets current through in forward direction
What does an LED do?
Gives off light when current passes through it in the forward direction
What is special about LDR's?
High resistance in the dark and low resistance in the light
What happens to a thermistor when temperature increases?
What are the positives and negatives of filament bulbs?
Good- cheap to make and buy
Bad- low energy efficiency
Only last 1200 hours
What are the positives and negatives of fluorescent bulbs?
Bad - only for 10000 hours
What are the positives and negatives of light emitting diodes (LED)
Lasts for 50000 hours
How do you calculate current?
How do you calculate potential difference ?
How do you work out the power of appliances?
Power (w) =. Energy (j)
What is mains electricity?
What does a cell give out? What type of current
How do you work out the frequency of a wave ?
Frequency = 1/ time interval
What are wires in cables made of and why?
Copper because they're good conductors of electricity
Why is the coating of wire made of plastic ? Why is it used?
Does not conduct electricity so stops us from getting electrocuted
Name the 3 wires in 3 pin plugs? What do they do?
Blue - neutral
Brown - live
Where do the wires go in a 3 pin plug?
sTriped - top
What does an earth wire do?
Stop us from getting electric shocks
Metal case attached to earth cable which is connected to ground by a rod
If fault causes the metal case becomes live
Big current flows through the case to the ground and causes fuse to melt shutting off the current
Why is a fuse? What does it do?
Thin piece of wire which conducts electricity
If current it too high the wire melts and current is cut preventing electrocution
How do you know which fuse is best?
Match the fuse to the appliance (slightly bigger)
What does a residual current circuit breaker do?
Detects difference between current in live and neutral wires
Shuts down current rapidly
What was the plum pudding model?
Region of positive charge with negative charges scattered in it
What was the nuclear model of an atom?
Positive nucleus with negative electrons surrounding
What do neutrons do?
Stop protons repelling each other
What is an isotope ?
Same number of protons different number of neutrons
What does it mean if an atom is radio active ?
Release radiation from its nucleus - decayed
Why can't you predict radioactive decay?
Totally random process - can't speed up or slow down
What does an alpha particle contain?
2 protons and 2 neutrons
What is a beta particle ?
Electrons produced in the nucleus and released
What is gamma radiation?
High energy electromagnetic wave
What were the results of the alpha scattering experiment?
Most alpha particles went straight through gold foil so most of an atom is empty space
Showed plum pudding model was wrong
Some particles bounces back - each atom must have small but heavy positive centre - repels
What is an alpha particles range in air?
5 cm before colliding with air particles
What is a beta particles range in air?
20cm in air
What is gamma radiations range in air?
What is alpha particles penetrating power?
Stopped by a single sheet of paper
What is beta particles penetrating power?
Stopped by few mm of aluminium
What is gamma radiations penetrating power ?
Several cm of lead to stop
What is an ion?
When atoms lose or gain electrons
What is the ionising power of radiation particles?
Alpha- very strongly ionising
Beta - white strong
How does radiation travel ?
How does radiation travel in a magnetic field
Gamma- passes in straight line (no charge)
Beta- deflected strongly (negative)
Alpha- deflected in opposite direction (positive charge) but not strongly as they are heavy
What is alpha radiation used for? How do they work?
Radioactive element releases alpha radiation
It's is very strongly ionising so when it collides with air particles it makes them charged (ions)
Ions move to oppositely charges plate and crates small current between plates
Smoke particles attach to ions and atom them from moving
Reduces current and sets off alarm
What is a use of beta radiation? How is it made?
Beta radiation passes through aluminium and is detected on other side
The rollers roll the aluminium to the correct thickness and this is tested by the amount of beta radiation let through
What is a use of gamma radiation? How are they used?
Radioactive dye is absorbed by tumour
Dye emits gamma radiation
Gamma radiation passes through body and can be detected on a scanner
How can gamma radiation treat cancer?
Gamma radiation is absorbed by cancer cells and kills them
What is half life?
Average time it takes for half of the nuclei to decay
What is background radiation caused by?
Buildings and the ground
What is nuclear fission?
When the nucleus of an atom splits
What is nuclear fission used for?
Generate electricity In nuclear power stations
What elements are used in nuclear fission?
How does nuclear fission occur?
Uranium or plutonium hit by a neutron
Nucleus splits into two smaller nuclei (radioactive)
Two or three more neutrons released
What is nuclear fusion?
Two atomic nuclei joint to make a large nucleus
Where does nuclear fission occur?
Suns and stars to release energy
Starts begin life as a cloud of dust and hydrogen gas
Gravity pulls them together causing gas atoms to get hot
Forms a protostar
What is the life cycle of a star if the stars the same size as the sun?
Main sequence star
What happens if a star is bigger than our sun?
Red super giant
Neutron star or black hole
Why isn't nuclear fusion used in power stations ?
Requires very high temperatures
What happens when two objects interact ?
Forces they exert on eachother are equal and opposite
What is the resultant force?
When a number of forces acting at a point can be replaced by a single force which has the same effect on the motion as the original forces al acting together
What can a resultant force do to an object?
Change its state of rest or motion
What happens if the resultant force on a stationary object is 0?
The object will remain stationary
What happens if the resultant force on a stationary object is not 0?
Object will accelerate in direction of resultant force
If resultant force acting on a moving force Is 0?
Object will move at same speed at same direction
What if resultant force on a moving object is not 0?
Object will accelerate in direction of resultant force
How do you calculate resultant force?
Force = mass x acceleration
What does the gradient of a distance time graph represent ?
What is velocity?
An objects speed in a given direction
How do you calculate acceleration?
Acceleration = change in velocity
What does the gradient of a velocity time graph represent ?
What happens when a vehicle travels at a steady speed?
Resistive forces balance the driving force
What happens to the breaking force as speed increases ?
A greater breaking force is needed to stop in a certain distance
What is the stopping distance of a vehicle ?
Thinking distance + breaking distance
How can a drivers reaction time be affected ?
What happens when breaks are applied ?
Work done by the friction force between the brakes and the wheel reduces kinetic energy of the wheel increases temp
What can vehicles breaking distance be affected by?
Adverse road and weather conditions
Poor vehicle conditions.
The faster an object moves through a fluid ....
The greater he frictional force that acts on it
Why will an object falling through a fluid initially accelerate ?
Due to the force of gravity
What is it called when an object falling through a fluid reaches a resultant force of 0?
How do you calculate the weight of an object?
Mass x gravitational field strength (10 n)
What can a force do to an object?
Change its shape
When happens when a force is applied to an elastic object ?
Object stretches and stores elastic potential
If An object is able to recover to its original shape when is elastic potential energy stored?
When woke is done on the object to change its shape
How do you work out the force applied to an elastic object?
F= spring constant x extension
What is work done?
When a force causes an object to move through a distance
How do you calculate work done?
W = force x distance
What is the unit of work done?
What happens when work is done?
Energy is transferred
What does power equal ?
P = energy
How do you calculate gpe?
Mass x gravitational field strength x height
How do you calculate kinetic energy?
1/2 x mass x velocity2
How do you calculate momentum ?
Mass x velocity
What is the conservation of momentum?
In a closed system the total momentum before an event = total momentum after an event
What are car safety features ? Name some
They absorb kinetic energy reducing momentum slowly. Reduces injury
Side impact bars
How do air bags work?
Air bags cushion the heard absorbing kinetic energy . Contains air which is slowly released
How do crumple zones and side impact bars work?
Gradually crush reducing momentum slowly