Summer Exams Flashcards
Charge=
Current X time
Q=IT
Voltage=
Current x resistance
V=IR
(Ohms law)
Electrical power=
Current x voltage
P=IV
Electrical power 2=
V=IR
P=I(squared)R
P=V(squared)/R
dfElectrical energy=
Current x voltage x time
E=IVT
Weight=
Mass x gravity
W=mg
Force=
Mass x acceleration
F=ma
Work done=
Force x distance
W=fd
Power=
Rate of doing work
P= W/t
Kinetic energy=
1/2mass x (speed) squared
1/2m(v)squared
Gravitational potential energy=
Mass x gravity x height gained
Gpe=mgh
Force=
..
F=kx
Force = spring constant x extension
Refractive index=
Sine angle of incidence/ since angle of refraction
N= sin i/ sin r
Sine (critical angle)
Sin c = 1/n
Pressure=
F/A
Force/area
Boyles law=
P1V1= P2V2
Series circuit
Simple circuit
When the different components are connected in a line
Can’t control which components current flows through
If u remove a component or it breaks then the whole thing stops working
E.g. Fairy lights
Parallel circuit
One on top of the other
If u remove or disconnect one of them, it will hardly effect the others
Ammeter rules
Ammeters are always connected in series, even in a parallel circuit
Voltmeter rules
Voltmeters are always connected in parallel with a component, even in a series circuit
Series components
Current same, voltage shared, add resistance to get total resistance
Parallel components
Voltage same, current shared in branches of circuit
Ohms law
V=IR
Newton’s second law force
f=ma
work also equals
change in energy
Conversion of energy in falling objects
GPE at start = KE at end
GPE will equal 0 and
KE will equal what the original GPE was
The earth wire
the earth wire is connected to the outer metal case of an appliance. if the live wire inside the appliance become s detached and touches the outer metal case, the outer metal case becomes live and hazardous to the user. The current rapidly flows around the metal case, to the earth wire and down to earth. once this happens, the appliance is no longer hazardous to the user because it is no longer connected to the live supply . Without the earth wire it could kill you.
Double insultation
Articles with plastic outer cases are referred to as being doubly insulated because they have the insulation of the electric cable and the the insulation of the plastic case to protect the user. For this reason it doesn’t need an earth wire. Diagram looks like a square inside a square.
Neutral wire
blue
live wire
brown
earth wire colour
yellow and green
Fuse
a fuse is a short piece of thin wire, which gets hot as current flows through it, if the wire gets too hot then the fuse melts, which breaks the circuit and switches off the current.
Circuit breakers
Modern consumer units have a main switch which will switch off all the circuits in the house in a very short time if an earth leakage current of more than about 25mA occurs. It detects when the current through two wires is different and breaks the circuit, which makes sure no people are harmed from the flow.
Circuit breakers V Fuses
Circuit breakers are easily re set, with the flick of a switch and there is no melted fuse wire to replace. The most important point is that circuit breakers can break an overloaded circuit much faster than a fuse can.
the most common defects likely to cause short-citcuting are:
- damaged plug, damaged insulation or frayed cabels
- overheating cabels
- damp conditions
- loosely connected wires
- long cables
- pushing metal objects into sockets
The earth wire and the fuse together protect
the appliance and the user
Resultant forces
whenever two bodies interact the forces they exert on each other are equal and opposite.
a number of forces acting on a body may be replaced by a single force, which has the same effect on the body as the original forces all acting together. This force is called the resultant force or unbalanced area.
Resultant forces questions eq
acceleration= unbalance force/ mass
unbalanced force=
either big arrow minus small arrow
or
if they are both travelling in the same direction then add the arrows
What factors affect the stopping distance of a car?
factors affecting thinking distance e.g. drugs and drinking
factos affecting braking distance e.g. road conditions and condition of car
Friction
friction is the force responsible for keeping nails and screws in different surfaces such as wood or walls
the direction of frictional forces is always opposite to the direction in which the object or surface is moving
friction causes objects to heat up and to wear away at any surfaces
friction acts when
an object moves through fluids such as air or water when solid surfaces slide across each other
air resistance
a friction force known as drag
opposed the motion of objects through air
water resistance
a friction force known as drag
opposes the motion of objects through water
Steps of a ball falling
it initially accelerated due to the force of gravity (which is called weight as it acts downwards)
as the object falls, it collides with fluid particles which exert upward frictional forces on the object
as the speed of the object increases, it collides with more particles per unit time
frictional forces increase in this way until they balance the gravitational forces
the resultant force eventually reaches zero and the body no longer accelerates
the body continues to fall at a constant speed, called the terminal speed.
Diagram of ball falling
6 balls
first one with just a downward arrow
the top arrow slowly grows on each diagram as the speed is increasing until the last one when both arrows are equal
Parachute graph start
parachutist leaves plane. The resultant force acting on the parachutist is the weight of the parachutist, which remains constant and acts towards the centre of the earth. the parachutist accelerates towards the earth at 9.8m/s2
Parachute graph middle of start and plateau
the drag force is increasing and the acceleration of the parachutist is less than 9.8m/s
Parachute graph plateau start
the drag force is equal to the weight of the parachutist. the resultant force acting on the parachutist is zero and the acceleration acting on the parachutist is also zero. the parachutist travels towards the earth at a constant velocity
Parachute graph plateau end before drop
the parachute is deployed and the drag force increases to a value that is greater than the weight of the parachutist. The resultant force acts upward and the parachutist experiences deceleration .
as the parachutist slows the drag force
decreases
parachute graph at the bottom of the drop
the drag force equals the weight of the parachutist and as the resultant force is zero, the parachutist travels at a constant velocity
parachute graph at the end of the plateu after the drop (the end)
the parachutist reaches the surface of the earth
Air- glass
i
refracts away from the normal
Air-glass
i=c
refraction takes place along the interface (angle of refraction =90)
air-glass
i>c
total internal reflection
when drawing angles…
remember to draw arrows in the direction that it is going
normal: 90 degrees to surface, get your ruler and put the line under the number on top of the line that the ray passes through, draw a horizontal line through it.
air-glass
opposites
draw the two on opposite sides of the shape then join up the normals in a slight slope in the middle
angle of incidence=
angle between the normal and the incident ray
one going in
angle of refraction=
the angle between the normal and the refracted ray
one that is coming out
law of reflection
angle of incidence=angle of reflection
c=
glass
42
c=
water
49
total internal reflection only happens when
ray travels from more dense to less dense
glass=
more dense
air=
less dense
total internal reflection is used for
endoscopes
optical fibers
Boyle’s law explination
for a fixed mass of an ideal gas at a constant temperature, if the volume of the gas is decreased, the pressure exerted by the gas will increase. The product of the pressure of the gas and the volume of the gas is a constant. e.g.= pV=constant
for a fixed mass of a gas at constant temperature
P1V1=P2V2
Pressure is measured in
Pa
or
N/m2
p=
f/a
Pressure in a gas
when particles collide with walls of containers, each collision exerts a force and pressure is therefore released on the walls of the container
the average kinetic energy of the particles in a substance is directly proportional to the kelvin temperature of the substance
if the gas is confined to a container and heated, then the molecules will possess a greater average kinetic energy
as a result their speed will increase more and the gas molecules will collide more often with the walls of the container, exert a greater force on the walls during each collision
pressure acts in
all directions
examples of pressure
breathing
aerosoles
Kelvin scale of temperature
t(k)=t(degrees c) +273
t(degrees c)= t(k)-273
0k=-273
energy of gas particles at absolute zero is
zero
kelvin temperature
is directly proportional to the mean (average) kinetic energy of gas particles
the kinetic theory of matter
based upon the following statements
1) all matter is made up of tiny particles called molecules
2) the molecules are in constant state of rapid, random motion
3) the higher the temp the more energy the molecules possess so the faster they move
evidence of kinetic theory of matter 1
1) diffusion: when one substance gradually spreads through another substance, it is diffusing through it. Examples include the diffusion of perfume throughout a room, if the top is left off the perfume bottle or the mixing with a drop of coloured dye placed in a glass of water
evidence of kinetic theory of matter 2
2) bownian motion: if a cell of air containing some smoke is illuminated and viewed under a microscope, the smoke particles can be seen moving about randomly in all directions in a jerky motion
hi charlotte
REVISSSSEE
how much electrical energy an appliance transfers relies on
how long the appliance is switched on
how fast the appliance transfers energy
whenever two bodies interact the factors they exert on each other are
equal and opposite
hookes law
provided the stretching force acting on an object does not extend the object beyond the elastic limit, the extension of the object is directly proportional to the stretching force
k
spring constant
