Paper 2

Question 1

How many volts come out of plug sockets?

Answer 1

230V

Question 2

What is the frequcency of generators spinning (europe)

Answer 2

50Hz

Question 3

Insulation causing charge

Answer 3

Friction causes a transfer of electrons, which carry a - charge

Question 4

Electrostatic induction

Answer 4

a negative charge is induced
(1)
on the part of the paper
closest to the comb (1)
opposite charges attract (1)

Question 5

Why is efficiency less than 100%

Answer 5

(useful) output energy is less
than input energy (1)
some energy is transferred to
less useful forms (1)

Question 6

Why do resistors heat up when current present

Answer 6

collisions between electrons and
lattice
allow collision between
electrons in this context
lattice {vibrates / moves} more

Question 7

National Grid

Answer 7

(long) transmission wires have resistance
* reduced p.d. at the destination
* (thermal) energy is dissipated in the
transmission wires
* this creates a power loss (refers to P=I
2R)
* transformers are used to step up to a high
voltage for transmission
* this means a low current (refers to VPIP=VSIS)
* so power loss is small(er)
* transformers used to step down to a safer
voltage for consumers
* consumer wires are shorter and so power loss is
less of an issue

Question 8

Why is a sprayed metal object connected to the floor with a wire

Answer 8

metal (wire) can conduct
electrons / charge (from earth)
(1)
(so) prevent (positive) charge
accumulating on object (

Question 9

How does earthing protect plugs

Answer 9

Earth
* earth wire connected to metal case
* metal case is a conductor
* (when live touches case) resistance between live
and earth is very low
* (very) large current to earth through (low
resistance) earth wire
* case is kept at same potential as earth
* so cannot get a shock if (earthed) person touches
metal case

Question 10

How do fuses protect plugs

Answer 10

Fuse
* made of thin wire
* fuse connected between live pin and wire to kettle
* temperature of wire depends on current in it
* when the current is (very) large, the temperature
of the wire increases beyond melting point of wire
* fuse (wire) breaks
* disconnects mains supply to kettle
* prevents damage to house wiring
* (now) there is no possibility of live wire in kettle
being at mains voltage

Question 11

How do you describe flemmings left hand rule

Answer 11

Thumb - force
Pointer - B
Middle - I
All held mutually Perpendicular

Question 12

How does a loudspeaker work

Answer 12

alternating current produces changing magnetic field
around coil
the coil is in a magnetic field of fixed magnets- produces a force (1)
the force on the coil /cone continuously changes
direction (1)
the paper cone /coil vibrates/
moves to and fro (1)

Question 13

The forces in the wooden block practical

Answer 13

Horizontal forces
* tension in the string/pull of the string
* tension is one of the horizontal forces acting on
the wooden block
* friction between the table and the wooden block
* friction acts in the opposite direction to the
tension
* friction opposes motion
* the force due to friction is equal to the force
provided by the tension
* the forces are balanced /equal and opposite
* no resultant force, so the block moves at a
constant (horizontal) velocity
Vertical forces
* (normal) reaction (force) upwards between the
table and the wooden block
* contact force
* weight of block downwards
* the weight (force of gravity) and the (normal)
reaction are equal and opposite / balanced
* the block does not move up or down
* tension caused by the force due to gravity on the
weight
* vertical forces on the block do not affect
horizontal velocity.

Question 14

How to change celcius to kelvin

Answer 14

+ add 273.14

Question 15

Why is the atmosphere more dense closer to sea level

Answer 15

greater density of atmosphere
greater depth of atmosphere
(above the aeroplane)
greater temperature (of the
atmosphere)

Question 16

What is the rule for when moments are in equilibrium around a pivot?

Answer 16

sum of the clockwise moments = sum of the anticlockwise moments

Question 17

Why does more current need thicker wires

Answer 17

thick(er) wires have low(er) resistance
= less thermal energy transferred
(in the wires)
allow so wires do not get hot
less potential difference /
voltage (drop) across the wires

Question 18

How do transformers work

Answer 18

magnetic field in primary / secondary coil / core (due to
current
magnetic field is alternating (this magnetic) field cuts/links secondary coil
induces an alternating voltage (across secondary coil) (1)

Question 19

What are the work transfers in engine jets

Answer 19

1. work is done against / by
   gravity (1)
2. idea of work done by the
   thrusters / jets (on the rover)
   (1)
3. (work done) by air/atmospheric
   resistance on the parachute
   (and rover) (1)
4. this reduces the kinetic energy
   (store) (1)
5. (there is a) decrease in the
   gravitational potential energy
   (store) of the rover (1)
6. (there is a) transfer of chemical
   energy from the thrusters (1)
7. energy transferred to thermal
   energy (store) (1)
8. (transfer) mechanically (to the
   thermal store) (1)

Question 20

National Grid

Answer 20

• Q is a step-up transformer
• step up V causes I to be lower
• voltage increases (25 kV to 400 kV)
• R is a transmission line / (national) grid /cable
• smaller currents in transmission lines
• less energy lost though heating those wires
• V = I x R
• smaller voltage drop across the transmission line
• S is a step-down transformer reducing
  voltage to 230V
• ready for use in homes T
• detail of transformers – iron core + coils
• transformers are not 100% efficient
• idea of power as V x I or P = I

Question 21

Loudspeaker / Microphone

Answer 21

Basic facts
* Sound is vibrations (of air)
* Loudspeaker emits / gives out sound
* Loudspeaker is an output device
* Microphone accepts / takes in sound
* Microphone is an input device
Principles of operation
* Alternating current or (electrical) signal sent
into a loudspeaker
* Loudspeaker cone / coil vibrates (air)
* Motor effect in loudspeaker
* Microphone cone / coil is vibrated by
air/sound
* Alternating current / (electrical) signal is
produced by microphone
* Electromagnetic induction in microphone
Details of operation of loudspeaker
* Alternating current or (electrical) signal in
coil produces changing magnetic field
* (changing) Force between magnetic field of
coil and magnet.
* Frequency / amplitude of sound depends on
frequency / amplitude of alternating current
Details of operation of microphone
* Coil oscillates in a magnetic field
* Generates an alternating p.d. (across the
wires) / alternating current /signal
* Frequency / amplitude of alternating p.d. /
current depends on amplitude / frequency of
the sound