Physics Fields Definitions PDF

Fields Definitions Force field- a region where an object experiences a non-contact force Radial field- a field where the field lines are all directed towards the centre and the magnitude of the field strength decreases with distance from the centre Uniform field- a field where the field lines are...

Fields Definitions Force field- a region where an object experiences a non-contact force Radial field- a field where the field lines are all directed towards the centre and the magnitude of the field strength decreases with distance from the centre Uniform field- a field where the field lines are parallel and equally spaced out Equipotential lines- lines of constant potential Gravitational Fields Newton’s Law of Gravitation- there exists an attractive force between two objects with the strength proportional to the masses of each object and inversely proportional to the distance between the centre of masses squared Gravitational field strength- the force per unit mass on a small mass in the field - gravitational field strength is a vector quantity Gravitational field lines- the direction of the force acting on a mass placed in a gravitational field g- the acceleration of an object due to gravity on the Earth’s surface or the gravitational field strength on the Earth’s surface Gravitational potential- the work done per unit mass required to move an object from infinity to that point in the field - gravitational potential is a scalar quantity - it has a negative value since gravity is an attractive force Potential gradient- the rate of change of potential - potential gradient is equal to gravitational field strength Escape velocity- the velocity required for an object to escape an orbit Geostationary orbit- an orbit in the equatorial plane with a time period of 24 hours - used for global communications - it is a synchronous orbit, as the orbiting body will stay in the same position above the Earth Synchronous orbit- an orbit with the same time period as the body it orbits Polar orbit- an orbit passing above both the North and the South pole - Used for weather monitoring and military surveillance Kepler’s First Law- objects orbit the Sun in an ellipse with the Sun at a focus of the ellipse Kepler’s Second Law- an object sweeps out equal areas of the ellipse in the same time period Kepler’s Third Law- the square of the time period of an orbit is proportional to the cube of the radius of the orbit (T2 ∝ r3) the a level physicist Electric Fields Coulomb’s Law- an equal but opposite force is exerted on two charged particles which is proportional to the charges of each of the particles and inversely proportional to the distance between the charges - opposite charges attract and like charges repel Electric field strength- the force per unit charge acting on a positive charge at a point in an electric field - electric field strength is a vector quantity Electric field lines- the direction of the force acting on a positive charge placed in an electric field Electric potential- the work done per unit charge required to move a positive charge from infinity to that point in the field - electric potential is a scalar quantity Potential gradient- the rate of change of potential - potential gradient is equal to electric field strength Capacitance Capacitator- a device used to store charge Capacitance- the charge stored per unit volt Charged stored-pd graph- a graph of charge stored (y-axis) against pd (x-axis) - the area under the graph equals the electric potential energy stored - the gradient is equal to the capacitance of the capacitator Time constant, 𝜏- the time required for the charge to drop to 37% of its initial value when discharging - 𝜏 = 𝑅𝐶 - the capacitator is effectively fully discharged or fully charged after five time constants Half-life, T1/2- the time required for the charge to half its initial value when the capacitator discharges Dielectric- the electrically insulating material between plates of the capacitator - the dielectric increases the capacitance of the capacitator Relative permittivity/ dielectric constant- the ability of a material to resist an electric field being formed within it the a level physicist Magnetic Fields Magnetic flux- magnetic field lines Magnetic flux density- the density of magnetic flux - can be thought of as magnetic field strength Tesla- the strength of a magnetic field that produces a force of 1 Newton in a wire of length 1m with 1 ampere flowing perpendicular to the field Magnetic field line- the direction of the force acting on a North pole in a magnetic field Motor effect- a current-carrying wire will experience a force in a magnetic field, as long as the wire is not parallel to the magnetic field liens Fleming’s left hand rule- a rule used to determine the direction of motion in a motor - thumb represents the motion of the current-carrying wire - first finger represents the direction of the field lines - second finger represents the direction of the conventional current Cyclotron- a machine used to accelerate particles - two semi-circular dees with a perpendicular magnetic field - an alternating pd accelerates the particle across the gap between the dees Solenoid rule- the North pole is at the end of the solenoid, when looking at the solenoid from the side, where the current flows in the anticlockwise direction Electromagnetic induction- an electromotive force is induced in a wire when it cuts across magnetic field lines Fleming’s left hand rule- a rule used to determine the direction of the induced current in a generator - thumb represents the motion of the current-carrying wire - first finger represents the direction of the field lines - second finger represents the direction of the (conventional) current generated Lenz’s Law- the direction of the induced current opposes the change that caused the current Faraday’s Law- the magnitude of the induced emf is equal to the rate of change of flux linkage throughout a circuit Magnetic flux linkage- the combined effect of the individual magnetic flux of each of the coils Alternating current- current that repeatedly reverses its direction Oscilloscope- a device used to observe a waveform The root mean square value of an alternating current, Irms- the value of direct current that produces the same heating effect as the alternating current in the same resistor the a level physicist Step-up transformer- a transformer with more turns on the secondary coil than the primary coil, which increases the voltage Step-down transformer- a transformer with less turns on the secondary coil than the primary coil, which decreases the voltage National grid- the network of transformers and cables that supplies electricity throughout the UK the a level physicist