Physics Flashcards
What are insulators?
- materials that inhibit the flow of electrical current
- the opposite of conductors, which allow electric particles to flow freely
What are conductors?
- substance where electrons, move easily from atom to atom
- with the application of voltage
What is conductivity? And examples of good conductors?
- the capacity to transmit something, such as electricity or heat
- Copper, steel, gold, aluminum, and brass
How are insulators charged?
- by friction (when they are rubbed together)
- a substance that gains electrons becomes negatively charged
- a substance that loses electrons becomes positively charged
Charging is caused by what?
Loss or gain of electrons
Like charges do what?
Repel
Unlike charges do what?
Attract
Applications of electrostatics
- one main use: printers and photocopiers where static electric charges attract the ink, or toner, to the paper
- other uses include paint sprayers, air filters, and dust removal.
Problems with static electricity
- can build up in clouds, can cause a huge spark to form between ground and cloud. Causes lightning – a flow of charge through the atmosphere
- dangerous when there are flammable gases or a high conc of oxygen - spark could ignite the gases + cause an explosion.
- dangerous when you touch something with a large electric charge on it - the charge will flow through body causing an electric shock
Describe what the dangers are of static electricity when refuelling aircraft tanks, what stops this from occurring?
- If the fuel passing along the hose to vehicle was allowed to build up a static charge, a resulting spark might ignite the fuel
- The hoses are earthed to stop this occurring
What does it mean for something to be earthed?
- connected to ground directly or indirectly so that electric charge flows from an object
- preventing dangerous build-up of static electricity
How is static electricity used in paint spraying?
- paint spray goes past a high voltage positive needle
as it leaves the spray gun - tiny droplets of paint pick up a positive charge (lose and e-)
- car body given a high voltage negative charge
which attracts the positively charged paint droplets
State two ways in why paint spraying using static electricity is efficient
1 paint droplets spread out more as they leave the gun - happens because they all get the same positive
charge and so they all repel each other
2 paint droplets attracted to negative
metal car body so less paint will be wasted
by landing on the floor
What is static electricity?
- an electrical charge produced by friction that causes sparks or crackling, can also attract dust and hair
Describe how static electricity is used in dust extraction
- used in pollution control
- by applying a static charge to dirt particles in the air and then collecting those charged particles on a plate or collector of the opposite electrical charge.
- device known as electrostatic precipitators
Why does smoke need to be removed and how is it done?
- power stations burn fossil fuels like coal and oil - smoke produced, smoke comprises tiny solid particles, like unreacted carbon, which can damage buildings and cause breathing difficulties
- Electrostatic precipitators
Describe (in 3 steps) how an electrostatic precipitator works
1 Smoke particles pick up a negative charge.
2 Smoke particles are attracted to the collecting plates.
3 Collecting plates are knocked to remove the smoke particles.
What’s an electric current?
- the rate of flow of electric charge
An electric current flows when?
- when electrons move through a conductor e.g. a metal wire.
Definition of current
- the flow of negatively charged electrons, from negative to positive
What’s ‘conventional current’?
- original definition of current (which is wrong)
- the flow of charges from positive to negative
Calculation for current
current (in amps) = charge in (coulombs) / time (in seconds) or I= Q/T I - current Q - charge T - time
What is amperes?
- amperes, amps, A is the unit of current
What is coulombs?
- coulombs, C is the unit of charge
What is voltage?
- measure of how much energy the electrons are carrying around to the things in the circuit
- measured in (V) volts
What is resistance?
- measure of how hard it is for the electrons to travel through a part of the circuit - measured in Ohms, Ω
Use of a voltmeter
- measures voltage (potential difference) across a component
Use of ammeter
- ammeter needs to measure the flow of charge, so it is in a series
- means that all the charge has to flow through it and can be counted
- also means that an ammeter needs to have a very low resistance
Why is a voltmeter in parallel?
- the voltmeter compares the energy difference between two points in a circuit, to see how much has been used up
- means it is in parallel
Why does the voltmeter need to have high resistance?
- otherwise all the current would flow through the meter instead of the component
Structure of a parallel circuit
- ## current divides into two or more paths before recombining to complete the circuit
Structure of a series circuit
- connected to a circuit in a way that same current flows through each component in turn
- opposite of in parallel
There is a resistance to the flow of an electric current through most what?
conductors
Resistance in a wire increases as what two things increase/decrease?
- the length of the wire increases
- the thickness of the wire decreases
What causes resistance in circuits?
- moving electrons colliding with the ions in the metal
- makes it more difficult for the current to flow therefore resistance
Describe the relationship between wire length and resistance
- resistance of a long wire is greater than the resistance of a short wire because electrons collide with more ions as they pass through
- relationship between resistance and wire length is proportional
Describe the relationship between wire thickness and resistance
- resistance of a thin wire is greater than the resistance of a thick wire because a thin wire has fewer electrons to carry the current
- relationship between resistance and the area of the cross section of a wire is inversely proportional.
What happens to current when resistance increases?
- when resistance is increased in a circuit, (e.g. by adding more electrical components) the current decreases as a result.
Calculating resistance equation
re-arrange this: voltage = current × resistance into R = V ÷ I R - resistance (Ω, Ohms) V - Voltage (V, volts) I - current (A, amps)
What increases as potential difference (voltage) increases?
- for given amount of electrical charge that moves, amount of energy transferred increases as potential difference increases
Calculating energy transferred equation
- energy transferred = potential difference × charge
- E = V × Q
E - energy (joules, J)
V - volts (amps, A)
Q - charge (coulombs, C)
How can volts be defined in terms of its equation?
one volt as one joule per coulomb
V = E / Q
x and y axis on a force-extension graph
x= extension (m) y= force (N)
describe the force-extension graph
- extension directly proportional to force applied (so steady increasing line)
- begins to plateau (change) at limit of proportionality and is now non-linear
limit of proportionality also referred to as?
- elastic limit
Where is non-linear extension and inelastic deformation seen on a force-extension graph?
- above limit of proportionality
gradient of force-extension graph before limit of proportionality shows what?
spring constant
what is the limit of proportionality ?
- furthest point material can be stretched/deformed while being able to return back to its original shape
What is Hooke’s law?
force = spring constant x extension
What’s elastic deformation?
- reversed when force removed
What’s inelastic deformation?
- not fully reversed when force is removed
- permanent change in shape
what’s extension(1) and what is compression(2) ?
(1) object increases in length
(2) object decreases in length
Units of spring constant (k) in Hooke’s law
N/m Newtons per meters
Units of extension in Hooke’s law
m Meters
- its the INCREASE in length
what does a higher spring constant indicate?
- a stiffer spring
energy stored in a spring is called what?
the elastic potential energy
elastic potential energy calculation
Ee= 0.5Ke(squared)
so 1/2 x spring constant x extension (sqaured)
State newtons first law
- if a body is at rest and the forces acting on it are balanced then the body will remain at rest
State newtons second law
force(N) = mass (kg) x acceleration (m s-2)
What’s inertia?
Inertia is a resistance to a change in motion
how does mass affect an object’s inertia?
more mass means more inertia
what’s needed to change the motion of an object with high inertia?
a greater resultant force
describe the motion of a car with 5000N drag and 5000N thrust
- forces acting on this car are balanced
- thrust is equal and opposite to the drag
- no net (resultant) force as the forces add up to zero
- car will be travelling at constant speed in a straight line
State Newton’s 3rd Law
- ‘if body A exerts a force on body B then body B exerts an equal and opposite force of the same type on body A’
