ALL OMAR'S MISTAKES

Explain why an aircraft is earthed before refuelling 2

Current must discharge (flow to the earth) first otherwise the bonding cable becomes unsafe as it becomes charged

Why is a metal object that is being spray painted need to be insulated from the earth? 1

To ensure it remains charged and doesn’t discharge

What are the two steps you should take to fully understand the question and what is required of you? 2

Read the command word carefully. Check the marks

A circuit breaker has a rating of 16A. Suggest a reason why the heater may switch off before it reaches its normal operating current. 1

Fuse might be rated less

What property of a wave determines the pitch of the sound? 1

frequency

Discuss the advantages and disadvantages of generating electricity using solar power and geothermal resources. 4

Advantages solar:

• renewable

• doesn’t release CO2 or SO2

Disadvantages solar:

• only works in sunny weather

Advantages geothermal:

• renewable

• no noise

• only requires a small amount of space

Disadvantages geothermal:

• can only be used in areas with geothermal rocks

A student stretches a rubber band. State the source of the energy transferred to the rubber band. 1

chemical store of the student’s hand

Explain how the graph shows that the rubber band does not obey Hooke’s law. 1

The extension is not directly proportional to the force applied because the gradient of the line is not straight

A current of 12A flows for 20 minutes in to an electric cooker. How much charge has the cooker used? 3

Q=It

Q=12×1200 —> 20 mins = 20×60=1200

=144000C

A student wants to investigate how the current through a filament lamp affects its resistance. Describe how the student could use her circuit (battery,variable resistor,lamp,voltmeter,ammeter) to investigate how the current through the lamp affects its resistance. 4

• Ammeter used to measure current

• voltmeter used to measure potential difference

• resistance of variable resistor altered to change current in circuit or change potential difference across the lamp

• resistance of lamp calculated for a large range of different currents that would allow a valid conclusion about the relationship to be made

people working with computer chips wear a bracelet with an earth wire. Name one suitable material that the bracelet could be made from with a reason. 3

• copper

• it is a metal so allows charge to flow because it is an electrical conductor

Enceladus has a similar orbital period to that of Deimos but its orbital speed is about 10 times larger. Explain how this is possible. 2

• The orbital radius of Enceladus is different to the orbital radius of Deimos

• Orbital radius of Enceladus is larger

Explain how cosmic microwave background radiation and red shift supports the Big Bang Theory. 5

• The further away a galaxy is, the greater the red shift

• The further a galaxy is the faster it is travelling away from us

• Distance and speed are directly proportional

• CMBR is present in all directions and parts of the galaxy implying that all parts of the universe were in contact a long time ago

• Wavelength of electromagnetic waves has increased implying that the universe was hotter a long time ago

explain how the diagram shows that the speed of the comet changes as it moves along its orbit. 3

• The diagram shows that the distance between the comets each week changes

• The time interval between observations is the same

• Because speed=distance/time, if the distance changes and the time stays the same then the speed also changes.

Suggest why the speed of the comet changes

• conservation of energy - As the comet loses gravitational potential energy (due to the sun’s gravitational force) it must gain kinetic energy

Explain why the gravitational field strength 11km above Mars was different to the surface of Earth. 2

• Mars has a smaller mass so has a smaller gravitational field strength

• Gravitational field strength changes with the distance from the object so 11km away would be different to on the surface

List the stages before a protostar. 3

• Cold cloud of dust and gas particles are attracted together due to the force of gravity

• A nebula is formed

• The temperature of the cloud increases

• The nebula collapses and forms a protostar

Evaluate how the thinking distance and the braking distance vary for different values of initial speed. 5

• They both have increasing distances as the initial speed increases

• Braking distance increases by a greater amount than thinking distance for the same initial speed

• Thinking distance had a linear gradient but braking distance had a non-linear gradient

• Thinking distance is directly proportional to initial speed

• Braking distance is proportional to initial speed squared

Explain how evaporation cools water. 3

• The temperature of the water is proportional to the average kinetic energy of the particles

• Highest energy particles escape as gas particles

• The average energy of the particles left in the liquid has decreased because the high energy particles are always leaving

The resistance of the filament lamp changes as the voltage is increased. Explain these changes in resistance. 3

• the lamp heats up

• The ions in the lamp gain kinetic energy which caused more chance of electron collisions

• Therefore the resistance increases

Suggest what can be deduced about the orbit of the moon as it oscillates over the month. 3

• The distance form the earth to the moon is not constant

• It is a cyclical relationship repeating each month

• Therefore the orbit of the moon is not circular

The orbit of the moon increases every year. What information does this give about the orbit of the moon? 2

• The orbital radius of the moon is increasing in all directions

• The moon is getting further away from the earth

an ice cube has a mass of 3.7g and the area in contact with the ground is 2.6 × 10^-4 m2. Calculate the pressure the ice exerts on the ground. 4

P = F/A

—- > 3.7g = 0.0037kg —- > F = mg —> F = 0.0037×10 = 0.037N

P = 0.037 / 2.6×10^-4

= 142Pa

The ice melts faster with a larger cross sectional area. Explain how the pressure changes when it melts. 3

• The area increases

• Weight is unchanged

• because pressure = force/area so the pressure would decrease

Explain the changes that occur when a solid melts

• Arrangement - Regular,fixed pattern to irregular pattern

• Movement - vibrating around a fixed point to sliding past eachother

• Bonds - Forces/bonds weaken

Explain the effect of driver tiredness on the thinking distance and on the braking distance of the car. 4

• Thinking distance:

  • Increases

  • The driver would have increased reaction times to apply the brakes once the hazard is seen

• Braking distance:

  • No effect

  • Has no effect on braking time of braking force