Physics Equations And Knowledge Flashcards
Formula for when there is a time, charge and current
Q = It
What formula to use when given a voltage, resistance and current
V = IR
What is voltage directly proportional to?
Current and/or resistance
As there is more light the resistance of an LDR….
Decreases
As the temperature of an ntc thermistor increases the resistance….
Decreases
Properties of an ideal diode
Perfect conductor when forward current and V, zero resistance with infinite current and no threshold voltage, opposite for opposite direction, e.g. no threshold voltage
Current and voltage rules for series
Current of all components is the same, voltage is the sum of all components (ratio)
Current and voltage rules for parallel
Total current is the sum of all current of the components, voltage is the same throughout in parallel
What formula to use when you have energy, voltage and charge
E= QV
Equation when you have voltage, power and current and how can this be changed if we have resistance instead of voltage
P= IV, since V= IR, P=I²R
What is the formula for energy transfer from power
E = Pt which can be re-arranged into E=VIt or E= I²Rt
Difference between hard and soft magnetic materials
Magnetically hard objects are ones that can be permanently magnetised and soft ones are objects that can be temporarily magnetised
What is induced magnetism?
When an object gains magnetism due to being kept/put in a magnetic field
What is the magnetic effect of a current?
If a current is flowing through a conductor, it starts to behave like a magnetic and therefore the current carrying conductor gets magnetised due to it
Magnetic field lines around a straight wire
Circular magnetic field, as you go out the weaker the field gets
Magnetic field lines around a coil/solenoid
Creates a type of North and south pole, + side of the battery is the south Pole of the field, - north pole
What factors affect the magnetic field strength
Type of metal used, amount of current flowing through the wire and temperature of the wire, as current increases the strength increases, as temp increases the strength decreases
What is the difference between permanent magnets and electromagnets?
Electromagnets are types of magnet that have a field produced by an electric current, permanent magnets are types of magnets that are made from hard materials that create their own persistent magnetic field
If a wire carrying a current is in a magnetic field, what can it experience?
A force
What factors effect the direction of a force in a magnetic field
The direction of the external magnetic field and the current flow
What factors affect the magnitude of the force on a wire in a magnetic field?
Force increases when current increases or the strength of the magnetic field increases.
In Fleming left hand rule, what do each of the thumb, first finger and second finger represent?
Thumb - Movement of force
First finger - Direction of the field
Second finger - Current flow
What equation is used to find the force of a wire in a uniform magnetic field
F = BIL (Force = magnetic field strength x current x length of wire)
Factors affecting the magnitude of the force/moment produced in a motor
Number of turns in the coil, current in the coil, strength of magnetic field
What occurs in a dc motor?
The coil is attached to a split ring commutator that has a gap in it to stop current flow when the coil is vertical and allow it to spin
Uses of electromagnets?
Magnetic elevators to lift heavy objects, maglev trains or data storage, transformers etc
What is induced when a wire cuts magnetic field lines?
A voltage/ potential difference
Factors affecting magnitude of induced voltage?
Speed of movement, field strength. Turns in coil, as all increase so does the voltage
Factors affecting the direction of voltage induced
Direction of relative motion between field and conductor or direction of field lines themself
What factors affect the output voltage of an a.c. generator?
Number of turns in the coil, strength of magnetic filed and increasing the rate of rotation
How does an a.c. generator work?
A coil is rotated in a magnetic field, a current is induced as a voltage also is induced, as it rotates the direction of the induced voltage changes direction, hence changing the current, slip rings connect to the coil and external circuit so a current can flow in the external circuit.
Applications of electromagnetic induction
A.c generators, dynamos (bike lights), microphones, loudspeakers/ headphones - motor effect
What is a step up and step down transformer?
A transformer designed to increase voltage from its primary to secondary is a step up transformer, a step down one is the opposite
What is the voltage ratio in a transformer?
Vp/Vs = Np / Ns
What is a consequence of 100% efficiency in a transformer?
Total transfer of electrical power so VpIp = VsIs or Vp/Vs = Is/Ip
What is the need for high voltage in power transmission?
We use step up transformers to increase voltage to thousands of voltage as due to P=IV, if voltage increases then current may decrease for a specific power, then, due to lower current, this means thay the energy lost is much less as heat energy wasted through resistance is proportional to current squared.
How would you calculate an energy loss in a transformer circuit?
P = I²R where R is given
Equation linking speed, time and distance
Speed = distance/time
Equation linking velocity, change in displacement and time
Velocity = Change in displacement /time
Equation for acceleration with change in velocity and time.
Acceleration= change in velocity / time
What is the equation for average speed
Average speed = total distance / total time
What is the equation with v² and u² in?
V² - U² = 2as
True or false, is there only one type of force?
False
What are some examples of different types of forces?
Weight, normal reaction, drag (including air resistance), friction, magnetic, electrostatic, thrust, upthrust, lift and tension
What is the elastic limit?
The elastic limit of a material is the furthest point it can be stretched or deformed while being able to return to its previous shape
What is elastic and inelastic extension
Elastic extension is where you can stretch a material with it returning to its original shape whereas inelastic extension is where the shape will not return back to what it was originally
What is hookes law and give the equation.
Hookes law was that the extension of an elastic object is proportional to the force applied up to a certain point, the equation is F = kx
What is the limit of proportionality?
The limit of proportionality refers to the point beyond which Hookes law is no longer true when stretching a material.
What are the two variations of the equation for energy stored in a stretched string?
E = 1/2 x Fx or E = 1/2 x kx²
What is newtons first law?
A body will remain at rest or in a state of uniform motion in a straight line unless acted on by a resultant external force.
What does mass resist?
Change in motion(inertia)
What is newtons second law and what are the equations for it?
Newtons second law is F = ma and suggests that the rate of change of linear momentum is directly proportional to the external force applied on the body. Which gives F = change in momentum / time
What is newtons 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 (every action has an equal and opposite reaction)
What is the difference between mass and weight?
Mass is constant and is scalar whereas weight can change and is dependent on the gravitational field strength and is a vector
What is the weight equation?
Weight = mass × gravitational field strength or W=mg
What happens in free fall?
A body will fall with acceleration equivalent to g
What factors affect air resistance?
The velocity at which the object is travelling at, the cross sectional area, the shape/surface of the body
How does terminal velocity come around and what forces are involved?
In free fall, objects accelerate downwards due to gravity, as speed/velocity increases, frictional forces such as air resistance and drag increase, at terminal velocity, the weight of an object due to g is balanced by the frictional forces as resultant = 0
What is the equation for momentum?
Momentum = mass x velocity or p=mv
What is and how do you do the law of conservation of momentum in one dimension
Momentum is conserved overall and therefore Total momentum = momentum before + momentum after