Physics AS/A level Paper 1

Topics 1, 2, 3, 6, 7 and 8

Centre of Mass

“The point at which the total mass of the object is said to act”

Conservation of Energy

“The energy of the system before an event = the energy of the system after the event“

Conservation of Momentum

“Momentum of the system before an event = the momentum of the system after”

Drag

“The resistance against the motion of an object. Usually proportional to the speed of that object”

Efficiency

Elastic collision

“Kinetic energy of a system before an event = kinetic energy after”

Equilibrium

“Moments about a point are balanced and the resultant force on the object is zero”

Force

“The rate of change of momentum of an object”

Gravitational potential energy

“The energy gained by an object when it is raised by a height in a gravitational field”

Impulse

• change in momentum

• Equal to the area under a force-time graph

• Force x change in time

• newton-second(N s)

Kinetic energy

• The energy an object has due to its motion

• The amount of energy that would be transferred from the object when it decelerates to rest

Momentum

“The product of an objects mass and its velocity”

Moment

The product of a force and the perpendicular distance from the line of action to the pivot about which the force is acting

Newton’s First Law

“An object at a constant velocity will remain at a constant velocity unless acted on by a resultant force”

Newton’s Second Law

“If an object is acted upon by a resultant force it will accelerate”

Newton’s Third Law

“Every action has an equal and opposite reaction”

Work Done

• A force applied over a distance

• Force x change in distance

Current

• “Rate of flow of charge”

• Change in charge over the change in time

• (Amps)

Potential Difference

• Work done per coulomb

• (Volts)

Resistance

• “A measure of how difficult it is for current to flow in a circuit “

• Directly proportional to the p.d.

• Inversely proportional to the current flow

• (Ohms)

Ohmic Conductor

“A conductor which follows Ohm’s law, the current flowing through is directly proportional to the potential difference, when it is held at a constant temperature”

Resistivity

• A measure of how easily it allows charge to flow through it

• ρ- Resistivity

• R- Resistance

• l- lenght

• (Ohm-metre)

Current and Potential

• n- number density(m^-3)

• q- the charge of charge carriers (usually 1.6×10^-16C)

• v- velocity of the charge carriers(ms^-1)

• A- cross sectional area of the wire(m²), calculate using A=πr²

Superconductor

“Materials which have zero resistivity at and below a critical temperature”

Semiconductors

Components for which the resistance changes depending on external conditions:

• LDRs- light sensitive

• Thermistors- temperature sensitive

Power

• “The rate of energy transfer”

• (Watt)

Filament Lamp

Diode

Series circuits

Total resistance:

Parallel circuits

Total resistance:

Kirchoff’s First Law

“The total current entering a junction is equal to the total current leaving it”

Kirchoff’s Second Law

“The sum of e.m.f in any loop of the circuit is equal to the sum of the p.d’s of each component”

E.M.F

• “The amount of energy supplied by the source per unit charge”

• (Volts)

Internal Resistance

“Opposition to the flow of charge within a cell”

Potential Divider

• A combination of two or more resistors in a series

• The p.d in the circuit is split into a specific ratio

Angle in radians

• s -arc length

• r -radius

Angular speed -ω

• v = ωr

Connecting period and frequency to angular velocity

• f = 1/T

• T = 2π/ω

• f = ω /2π

• ω = f2π

Centripetal force

“We know from Newton’s first law that to accelerate, an object must experience a resultant force, therefore an object moving in a circle must experience a force”

• It always acts towards the centre of the circle

Centripetal acceleration

“The acceleration experienced while in uniform circular motion”

Simple Harmonic Motion

• An object is experiencing SHM when its acceleration is directly proportional to displacement and is in the opposite direction”

• x is the displacement from the equilibrium position

Electric Field

• “A region of space in which an electric charge experiences a non-contact force. This force can be attractive or repulsive”

Coulomb’s Law

• Determines the force acting between two charges.

• If the force has a positive value, it is a repulsive force

• If the force has a negative value, it is an attractive force

• F - electric force

• Q₁ and Q₂ - charges

• r - distance of separation

Electric Field Strength (E)

“The electrostatic force that a unit positive charge would experience, at a given point in the field”

Radial Field

• The field is stronger nearer the surface of the object, and weakens as you move further away

• For a positive charge, the arrows point outwards

• For a negative, the arrows point inwards

Uniform Field

Exerts that same electric force everywhere in the field

Electric Field Strength Equations

• The first equation is for a radial field

• Second is for a field formed by parallel plates

• V- voltage

• d- distance between the plates

Electric Potential

“The amount of work done in moving a unit positive charge from infinity to that point”

• k- Coulomb constant

• Q- charge

• r- distance of separation

Electric potential difference

The work done moving a positive charge from one point to another

Capacitance (C)

The amount of charge a capacitor can store per unit of p.d

• (Farads)

Energy stored by a capacitor

The second and third equations are derived by substituting the capacitance equation into the first

Energy stored by a capacitor- graph

• Area under a charge-voltage graph gives the energy stored

• The gradient of the graph is the capacitance

Charging graph for a capacitor

Discharging graph for a capacitor

Capacitor discharging

• Q₀ is the initial charge…

• To simplify the first three equations, take natural logs of both sides

Time Constant

• The product of the resistance in the circuit and the capacitance of the capacitor

• The time taken to charge the capacitor to 1-1/e of its final value

• The time taken to discharge the capacitor to 1/e of its initial value

Magnetic Flux Density

• A measure of the strength of a field

• (Tesla)

Motor Effect

Is when a current-carrying wire experiences a force in a field

Motor Effect- magnitude of the force

• B- Magnetic Flux Density (T)

• I- current (A)

• L- length of wire (m)

Fleming’s Left Hand Rule

• Direction of the force experienced by a current-carrying wire

• Forefinger: point in the direction of the magnetic filed

• Middle finger: the direction of the current

• Thumb will be pointing in the direction of the force

Magnetic Flux

“A measure of the magnetic field that passes through a given area”

• Magnetic Flux (Wb) = Magnetic Flux Density (T) x Area (m²)

• This applies if the magnetic field lines are perpendicular to the area

Magnetic Flux Linkage

• more useful if using a coil

• N Φ = B A N cos ⁡ θ

• N- number of turns