incorrect exam questions Flashcards
why does a magnet fall more slowly in a copper tube?
- force on magnet
- force opposes the motion OR force on magnet due to magnetic field caused by current in tube
why very high temp needed to force two H nuclei together?
- high temperature produces high energy
- the molecules repel eachother
- both are postively charged/have like charges
What happens to the light after it passes the lens
- is focused
- travels toward a point
- diverges or spreads out from that point
how energy from the sun to be warming roads
- radiation
- light/infrared
- travel through space
- absorbed by road
cool wind how
- density decreases and air rises
- air is replaced by cool air
evaporatop
- higher speed molecules escape
- adverage kinetic energy of the molecules decreases
- temeprature is related to speed
why metals can conduct electricity
atoms vibrate and hit the delocalied electrons
electrons travel through the metal and hit atoms
transferring heat
how to use a stop watch to determine the time period of the pendulum
- use stop watch to time oscillations
- use of fiduciary aid to detemine a complete cycle
- use of multiple oscillations and division
How a gas exerts a pressure:
- moving particles hit walls
- momentum changes when particles hit walls
- force exerted by particles due to rate of change of momentum
- P = F/A
How does thermal energy transfer to worker whos of a distance to the metal
- By radiation
- EM waves, like infrared, travel to the worker
- are absorbed by the worker
why would magnet move left if north to north?
force is in the direction of the field
specific latent heat of fusion
energy transferred when 1kg of a substance freezes or melts
why mixture of ice and water remain at a lower temp after 10 mins than mixture of water
energy is needed for change of state so temperature doesn’t rise until this has taken place
mixture of ice and water will remain at 0 until all ice has melted
Explain, in terms of molecules, how the evaporation of sweat cools the person.
- in evaporation more energetic molecules escape
- lower energy molecules remian so remaining liquid is cooler
- thermal energy is taken from person to liquid
how does wind increase evaporation?
wind blows fast moving molecules away OR ensure molecules do not re-enter the liquid
if wider gap, what happens to waves in diffraction?
waves will pass through gap, remaining straight
as less diffraction occurs
EMF definition
energy supplied to drive a unit charge round a complete circuit
safety precautions which hospital staff taken when workiing with y-ray sources
- store in lead lined boxes
- limit expsoure time
- stand behind wall
- don’t let pregnant staff to work
Iodine-131 emits γ-radiation. It has a half-life of 8 hours.
Explain why this emission and this half-life make iodine-131 a suitable material for a tracer in medical diagnosis.
- y can be detected outside the body
- long enough half life to be detected
- short enough half life to soon have very little activity
- weakly ionising or pass out of body without harm
kWh
energy transferre in one hour at the rate of transfer of 1kW
Explain, in terms of forces and distances between particles, why the gas occupies a much greater volume than it does as a liquid.
Forces between particles are much greater in liquids than gases
Particles in gases are further apart
) We can see light from the Sun but we cannot hear any sound from it. WHY
sound needs a medium to travel through
light doesnt need a medium to travel through
voltage
work done in passing a charge through a component
EMF formula
W/Q = E
work done/charge = emf
Explain what happens in the circuit you have drawn in (c)(i) when the temperature of the thermistor is increased.
resistance decreases
resistance in circuit decreases
current in circuit increases
how determine direction of force in a motor
- current, magnetic field, motion at right angles to eachother
- magnetic field is from north to south
- current is from positive to negative
State and explain what happens to the coil as it reaches the vertical position.
- (at the vertical) the coil stops
- (at the vertical) turning effect is zero
Effects of split ring commutator and the brushes
- brushes ensure the current is maintained
- coil rotates continuously
- without wires getting tangled
- every half turn
nuclear fission
when a neutron hits a large and unstable nucleus, splitting the nucleus into smaller nuclei and releasing large amounts of energy
nuclear waste (+) and (-)’s
(+) continuous supply of energy
(+) not affected by weather
(+) produces large amounts of energy
(-) not renewable
(-) danger if any leak of radiation
(-) produces hazardous waste
Explain, in terms of molecules, how sweating helps to cool your body on a hot day
- energy in the skin is transferred to sweat
- these molecules have enough KE to escape from the skin and become water vapour
- leaving behind molecules with lower energy
- which leaves the skin at a lower temperature
The heating element in Fig. 4.1 remains switched on. The temperature of the sand remains constant at a value above room temperature.
Explain why the temperature of the sand remains constant.
- Energy is constantly lost from the sand to the surroundings
- the rate of energy supplied to sand is equal to the rate of energy lost from the sand
difference between slip and split rings
slip rings => generators
split rings => dc motors
Explain how rotating the coil in Fig. 6.2 continuously causes the galvanometer needle to show an alternating current.
it cuts field between the magnets
inducing an emf
this produces a current in the galvanometer
direction of current flow changes with each 180 degree rotation of coil
Explain the operation of a basic transformer.
An alternating current in the PC
Produces a changing mangetic field
Field induces an EMF in secondary coil
Describe how the americium-241 ionises air.
Alpha particles (emitted from americium) hit molecules in the air and remove electrons
Suggest and explain two reasons why smoke detectors use an isotope that emits α-particles rather than an isotope that emits γ-radiation.
- Alpha not penetrating and is stopped by smoke particles
- alpha more highly ionising and ionises the air more easily
- short range so less harmful to humans
Explain, in terms of the particles of the metal, why the decrease in the volume of the metal is less than that of the gas.
- forces between particles are larger than gases
- particles are closer together OR are already touching
Explain why the red light does not change direction as it enters the plastic block.
angle of incidence = 0 so angle of refraction = 0
difference and similiarites between emf and pf
both relate to energy per unit charge (E = W/Q)
emf applies to the whole circuit, while pd applies to one component
lamp get brighter why (thermistor and potential divider question)
the resistance of thermistor reduced
voltage increases
current in lamp increases
why light changes direction (refraction)
one side of the wavefrot enters the solid first
the side slows down first
the other side continues to move at the original speed causing turning
