Oxford Revise AQA GCSE Physics | Chapter P15 answers

P15: Electromagnetic waves

Answers

Extra information

Mark

AO / Specification reference

01.1

one from:

  • radio
  • microwave
  • infrared
  • visible

1

AO1

4.6.2.1

01.2

one from:

  • x-rays
  • gamma rays

1

AO1

4.6.2.1

01.3

one from:

  • premature skin aging
  • increase risk of skin cancer

1

AO1

4.6.2.3

01.4

wear clothing/hats/sunscreen

1

AO3

4.6.2.3

02.1

the sheets absorb radiation

less radiation produces a lower potential difference

1

1

AO3

02.2

\(\rm{ignoring\ outlier},\ \frac{3.74 + 4.40}{2} = 4.07\)

1

AO2

02.3

sensible suggestion and solution e.g.,

background light from room lights/sunlight; will always produce a potential difference even when the lamp is off

so carry out the experiment in a dark room/reduce the amount of background light within the room

1

1

AO3

02.4

gamma rays are ionising

which can cause mutations and cancer

1

1

AO2

4.6.2.3

02.5

visible light is produced when electrons move between the energy levels in atoms

gamma rays are produced by changes in the nucleus/when the nucleus decays

1

1

AO1

4.6.2.3

03.1

x-rays are ionising

so can increase the risk of cancer/damage DNA in cells

1

1

AO1

AO2

4.6.2.3

03.2

a measure of the risk of harm resulting from an exposure of the body to radiation

1

AO1

4.6.2.3

03.3

the foot x-ray is a single x-ray, whereas a CT scan consists of multiple x-rays

1

AO2

4.6.2.3

03.4

\(
\begin{array}{l}
\textrm{number of foot x-rays } = \frac{2}{0.001}\\
= 2000
\end{array}
\)

1

1

AO2

4.6.2.3

03.5

\(
\begin{array}{lr}
\frac{15}{2.7}\\
= 5.5\ \rm{years}
\end{array}
\)

1

1

AO2

4.6.2.3

04

Level 3: Describes how infrared/radio are used with reasons, describes risks of X-rays/gamma, and their uses. Well organised answer.

5-6

AO1

AO2

4.6.2.4

Level 2: Describes how infrared/radio are used without clear reasons, describes risks of X-rays/gamma, but not their uses. Some organisation.

3-4

Level 1: Some uses and waves described, answer not well organised, uses or reasons missing.

1-2

No relevant content.

0

Indicative content:

  • televisions use radio waves because you can add information to the waves
  • televisions receive the radio waves and convert them to light and sound
  • heaters emit infrared radiation
  • the radiation is absorbed by the air and raises the temperature of the house
  • energy efficient lamps emit ultraviolet radiation
  • there are no household uses of X-rays and gamma rays
  • because they are ionising and increase the risk of cancer

05.1

visible light

1

AO1

4.6.2.1

05.2

words in this order:

transverse

300 000 km/s

longitudinal

340 m/s

energy

matter

lose one mark for each incorrect word

5

AO1

4.6.2

05.3

radio

1

AO1

4.6.2.1

05.4

satellite communication/mobile phones/radar

1

AO1

4.6.2.4

06.1

06.2

one mark for three parallel wave fronts above horizontal line/in medium 1

one mark for wave fronts perpendicular to ray

one mark for three parallel wave fronts below horizontal line in medium 2

one mark for wave fronts perpendicular to ray

one mark for larger wavelength than in medium 1

2

3

AO2

AO3

4.6.2.2

06.3

the frequency stays the same

the speed increases

1

1

AO2

AO3

4.6.2.2

06.4

any correct situation e.g.,

light waves moving from glass/perspex/water into air

1

AO3

4.6.2.2

07.1

radio waves – television/radio

microwaves – satellites/mobile phones

1

1

AO1

4.6.2.4

07.2

x-rays

to look at broken bones

accept any correct use of medical x-ray imaging

1

1

AO1

4.6.2.4

07.3

visible light is produced by movement of electrons in atoms

gamma rays originate from changes in the nucleus of an atom

1

1

AO1

4.6.2.3

08.1

4 seconds

the car changes from moving at a constant speed to decelerating

1

1

08.2

distance = velocity × time/area under the graph

= 10 × 4

= 40 m

1

1

AO1

AO2

4.5.6.1.2

08.3

\(
\begin{array}{lr}
\rm{acceleration}\ = \frac{\rm{change\ in\ velocity}}{\rm{time}}\\
\rm{acceleration}\ = \frac{0-10}{2}\\
= -5\ \rm{m/s}^2
\end{array}
\)

answer is negative because the car is decelerating

measurements from the graph

1

1

1

AO1

AO2

4.5.6.1.5

08.4

\(\rm{the\ acceleration\ is}\ \frac{-2-0}{2} = -1\ \rm{m/s}^2\)

it is in the opposite/reverse direction/ is five times smaller

answer must show evidence that the negative acceleration (in the opposite direction) is five times smaller

1

1

AO2

AO3

4.5.6.1.5

09.1

you can use a model to predict or explain

not just describe what happens

1

1

AO1

09.2

by producing the electromagnetic waves and then detecting them Hertz showed that the model was correct

1

AO2

09.3

the electromagnetic wave causes the electrons in the aerial to oscillate

the oscillations produce an alternating current

with the same frequency as the radio wave

1

1

1

AO1

AO2

4.6.2.31

10.1

black clothing gets hotter faster because it absorbs thermal radiation/energy faster than white clothing

1

AO2

4.6.2.2

10.2

correct suggestion e.g. mirror/foil blankets provided after marathons/foil used in cooking

1

AO2

4.6.2.2

10.3

two from:

  • the starting temperature of the water
  • the volume of water
  • material of can

one mark for each correct answer up to a maximum of two points

2

AO2

4.6.2.2

10.4

one mark for two curved lines with negative gradients

one mark for starting at same temperature

one mark for silver line above black line

one mark for labelled axes

4

AO2

4.6.2.2

10.5

no

the silver can emit radiation as it cools down, but not as fast as the black one

1

1

AO2

4.6.2.2

11.1

400 – 750 nm

1

AO2

4.6.2.1

11.2

heat absorbing glass two

at that wavelength the light transmitted is the lowest, so the light absorbed is the biggest

1

1

AO3

4.6.2.2

11.3

heat absorbing glass one is the best

it transmits the highest percentage of radiation in the range 430 nm and 662 nm

1

1

AO3

4.6.2.2

11.4

no

to get a suntan you need to absorb ultraviolet radiation

tis very little ultraviolet radiation transmitted by the glass at that wavelength

1

1

1

AO2

AO3

4.6.2.4

12.1

\(
\begin{array}{lr}
\rm{speed}\ = \rm{frequency\ \times\ wavelength}\\
300\;000\;000 = \rm{frequency}\ \times\ 2 \times\ 10^{-10}\\
\rm{frequency} = \frac{{{\rm{300\ 000\ 000}}}}{{{2} \times {1}{{0}^{{\rm{-10}}}}}}\\
= 1.5\ \times\ 10^{18}\ \rm{Hz}
\end{array}
\)

accept v = f × λ

one mark for conversion to m/s and one mark for substitution

1

1 + 1

1

1

AO1

AO2

4.6.1.2

12.2

order of magnitude: 1018Hz

1

AO2

4.6.2.1

12.3

\(
\begin{array}{lr}
10\ \rm{cm} = 0.1\ \rm{m}\\
= \frac{300\;000\;000}{0.1}\\
= 3 \times 10^9
\end{array}
\)

1

1

1

AO1

AO2

4.6.2.1

4.6.1.2

13.1

the frictional force of the brakes (and air resistance) acts on the car

water resistance (and air resistance) acts on the boat

1

1

AO2

4.5.1.4

13.2

up arrow: upthrust

left arrow: water resistance/drag force

right arrow: weight

one mark for two equal length arrows pointing up and down

one mark for labels for upthrust and weight

one mark for single arrow pointing left

one mark for labels for drag and water resistance

4

AO1

AO2

4.5.1.4

13.3

kinetic energy = 0.5 × mass × speed2

= 0.5 × 1500 × 162

= 192 000 J

\(\textrm{allow E}_{\rm{K}} = \frac{1}{2}\rm{mv}^2\)

1

1

1

AO2

4.1.1.2

13.4

(using the conservation of energy) work done by friction = kinetic energy

\(
\begin{array}{lr}
\rm{kinetic\ energy\ (work\ done)} = \rm{force}\ \times \rm{distance}\\
192\;000 = \rm{force} \times 100\\
\rm{force} = \frac{192\;000}{100}\\
= 1920\ \rm{N}
\end{array}
\)

force on car is bigger

same kinetic energy loss but it stops over a smaller distance/there is reaction time so the braking distance is smaller than 30 m

1

1

1

1

1

1

AO1

AO2

AO3

4.5.2

14.1

\(
\textrm{acceleration = }
\frac{{{\rm{change\ in\ velocity}}}}{{{\rm{time}}}}
\)

accept a = (∆v)/t

1

AO1

4.5.6.1.5

14.2

\(
\begin{array}{lr}
\textrm{acceleration = }\frac{2.7-0.5}{0.4}\\
= -5.5\ \rm{m/s}^2
\end{array}
\)

1

1

AO2

4.5.6.1.5

14.3

force = mass × acceleration

accept F = ma

1

AO1

4.5.6.2.2

14.4

\(
\begin{array}{lr}
2.0 = 0.4 \times\ \rm{acceleration}\\
\textrm{acceleration =}\frac{{{2}{\rm{.0}}}}{{{0}{\rm{.4}}}}\\
= 5.0\ \rm{m/s}^2
\end{array}
\)

1

1

1

AO2

4.5.6.2.2

14.5

there is an uncertainty in all measurements but maybe more uncertainty in the force and mass than in the light gate measurements/difficult to pull with a constant force so acceleration may not be constant

1

AO3

4.5.6.1.5

4.5.6.2.2

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