Physics Definitions Unit 4

Capacitance, gravitational fields and Orbits, Doppler, Dark Matter, Electrostatic fields, Physics of sport, Electromagnetic induction

Capacitance (Capacitance)

Charge stored per unit volt (Q/V)

What is capacitance proportional to? (Capacitance)

Area of plate

Area under a VQ graph (Capacitance)

work done

Capacitor combination in Series (Capacitance)

C+C

Capacitor combination in parallel (Capacitance)

1/C +1/C

Time constant for discharge (Capacitance)

Time taken for current/pd/charge to fall to 37% original value

Time constant for charging (Capacitance)

time taken for the current/pd/charge to fall to 63% original value

What type of decay happens during charging and discharging (Capacitance)

Exponential

Inverse square law of gravitational fields (gravitational fields)

The force between two masses is proportional to the product of their masses and is inversely proportional to the square of their distance apart

F∝ mxm

F∝1/r²

Gravitational field (gravitational fields)

region where a mass experiences a force

Gravitational field strength (gravitational fields)

force per unit mass at that point

Is gravitational field strength vector or scalar? (gravitational fields)

Vector

What is the direction of the gravitational field strength given by? (gravitational fields)

The direction of the force acting on the mass in the field

Uniform gravitational field (gravitational fields)

field with the same size and direction at all points

Gravitational potential energy (gravitational fields)

energy a body has because of its position above the ground

what type of field does mgh apply to? (gravitational fields)

Uniform

Non-uniform gravitational field (gravitational fields)

where size and/direction of field changes within the field

Equipotential Surfaces (gravitational fields)

spheres around a planet where the radius is constant - so potential is constant

Radial Field (gravitational fields)

Field produced by a spherical mass (both size and direction alters)

Gravitational potential (gravitational fields)

Work done in bringing a mass from infinity to that point per unit mass

What is the potential at infinity? (gravitational fields)

0

Gravitational potential energy (gravitational fields)

Work done in bringing a mass from infinity to that point

Gravitational potential energy for a system of 2 masses (gravitational fields)

work done in bringing either (or both) of the masses from infinity to that separation (r)

Why are GPE and potential negative (gravitational fields)

Because the field does the work (masses are attracted to each other)

e.g. you don’t have to do work to make and object fall to earth (gravity does that)

K1 Law (Orbits, Doppler and Dark Matter)

The orbit of every planet is an ellipse with the star at one focus

K2 Law (Orbits, Doppler and Dark Matter)

The radius vector (from the sun to the planet) sweeps out equal areas in equal time

K3 Law (Orbits, Doppler and Dark Matter)

The square of the period of orbit (T) is directly proportional to the cube of the semi-major axis (r)

Semi-major axis (Orbits, Doppler and Dark Matter)

Half the major axis

Major axis (Orbits, Doppler and Dark Matter)

longest diameter in an eclipse

Semi-major axis in a circle (Orbits, Doppler and Dark Matter)

radius

What type of force is the force between two masses (Orbits, Doppler and Dark Matter)

ALWAYS attractive

G (Orbits, Doppler and Dark Matter)

universal constant of gravitation

What accounts for missing mass in the universe?(Orbits, Doppler and Dark Matter)

Dark matter

Extended response for evidence of dark matter (Orbits, Doppler and Dark Matter) 4 points

• measured velocities too high (from graph)

• according to equation, line should drop off as 1/√r

• ∴ we have extra mass

• extra mass = dark matter

What could be an explanation for dark matter? (Orbits, Doppler and Dark Matter)

Higgs Boson

Doppler Effect (Orbits, Doppler and Dark Matter)

When received frequency differs from actual frequency due to movement of the object

When is received frequency higher? (doppler)(Orbits, Doppler and Dark Matter)

When object is moving closer

When is received frequency lower? (doppler)(Orbits, Doppler and Dark Matter)

When object is moving away

When do we get red shift? (due to doppler) (Orbits, Doppler and Dark Matter)

Object moving away

When do we get blue shift? (due to doppler) (Orbits, Doppler and Dark Matter)

Object moving closer

Gradient of what graph gives Hubble constant? (Orbits, Doppler and Dark Matter)

How fast galaxy is moving away by how far away galaxy is

Hubble Constant (Orbits, Doppler and Dark Matter)

Expansion rate of the universe

1/ hubble constant (Orbits, Doppler and Dark Matter)

age of the universe

open universe (Orbits, Doppler and Dark Matter)

universe continues to expand forever

kinetic energy to spare after reaching infinity

closed universe (Orbits, Doppler and Dark Matter)

gravity of galaxies too great and pulls the universe back into big crunch!

Flat Universe (Orbits, Doppler and Dark Matter)

universe continues to expand but comes to rest at infinite size (escape velocity theory)

Electric Field (Electric fields)

region where an electric charge experiences a force

electric field strength (Electric fields)

force acting on a unit positive charge placed at that point in the field

What is direction of electric field given by? (Electric fields)

the direction a positive charge would move if placed in the field at that point (conventional current)

Where is all charge concentrated in a sphere? (Electric fields)

centre

Direction of radial field from positive charge? (Electric fields)

Out

Direction of radial field from negative charge? (Electric fields)

In

What happens to the strength of radial fields when you get further away (Electric fields)

get weaker

What are stronger: magnetic fields or electric fields? (Electric fields)

Electric fields

Are Radial fields uniform? (Electric fields)

No

Uniform electric field? (Electric fields)

doesn’t vary in size or direction

Direction of electric fields? (Electric fields)

Positive to negative (with conventional current)

potential difference between two points (Electric fields)

work done per unit charge in moving from one point to another

potential at a point (Electric fields)

work done in bringing unit positive charge from infinity to that point

Is potential a scalar or vector? (Electric fields)

scalar (ignore direction)

What two things are assigned a potential of 0? (Electric fields)

Infinity and Earth

Equipotential (Electric fields)

a line joining points in an electric field which have the same potential

Where are equipotentials in relation to the electric field lines? (Electric fields)

at right angles

What does the gradient of an electric potential against distance graph give you? (electric fields)

potential gradient

What does the negative potential gradient give you? (electric fields)

electric field strength at that point

What are B-fields produced by? (Magnetic fields)

permanent magnets or currents

which way do field lines go? (Magnetic fields)

North → South

What is a solenoid? (Magnetic fields)

Long coil of wire - such that length is much bigger than diameter

What is μ₀ ? (Magnetic fields)

permeability of free space

n (Magnetic fields)

number of turns per meter

What fields do static vs moving charges cause?

static - electric

moving - magnetic

what direction does conventional current flow?

positive to negative

What direction do electrons flow?

negative to positive

What is magnetic flux density also known as? (Magnetic fields)

Magnetic field strength

B-field strength

B (Magnetic fields)

force per unit length of current carrying wire

At what angle is force maximum in a B-field?

90 (sinθ = 1)

Why does a mass spectrometer have slits? (Magnetic fields)

to narrow the electron beam

What happens in section 1 (velocity selector) of a mass spectrometer? (Magnetic fields)

electric force = magnetic force ∴ straight line motion

What happens in section 2 (detection) of a mass spectrometer? (Magnetic fields)

no electric force ∴ no equilibrium ∴ particle in circular motion due to B-field

Area used in Hall probe calculations? (Magnetic fields)

area that current goes into

What do we use a hall probe to measure? (Magnetic fields)

B-field

What placed inside a solenoid increases magnetic field strength? (Magnetic fields)

An Iron core (up to 200,000 times for pure iron)

Electron volt (Magnetic fields)

energy gained by an electron when accelerated through a pd of 1V

What type of acceleration do particles experience in a particle accelerator? (Magnetic fields)

constant

3 types of particle accelerators? (Magnetic fields)

• linear accelerator (Linac)

• cyclotron

• synchrotron

Centre of Gravity (physics of sport)

point at which the weight of the object seems to act

2 things that increase stability (physics of sport)

1. lower centre of gravity

2. wider base

What leads to toppling?

When line of action of weight is outside the base

Moment of inertia (I) (physics of sport)

reluctance of an object to stop spinning around an axis

Angular acceleration (⍺) (physics of sport)

rate of change of angular velocity

L (physics of sport)

angular momentum

principle of conservation of angular momentum (physics of sport)

total angular momentum of a system with no external resultant torque remains constant

what does it mean when theres no slipping (e.g when a ball is rolling down a hill) (physics of sport)

velocity of the point of the ball touching the ground is zero

(forward velocity of CoM of the ball must cancel the rotational velocity at that point)

Why does a rolling object not accelerate with gsinθ? (physics of sport)

less acceleration because some of the energy goes into rotational KE rather than purely linear KE

what happens to pressure at high speeds? (physics of sport)

decreases

Drag (physics of sport)

resistive force that always acts in the opposite direction to the motion

Magnus Effect Force (physics of sport)

lift - at right angles to the direction of motion and its at right angles to the axis of rotation

Magnetic Flux (Electromagnetic Induction)

BA with B-field strength at 90° to coil of area A

ɸ (Electromagnetic Induction)

Magnetic Flux

Magnetic Flux Unit (Electromagnetic Induction)

Webers (Wb)