HP Remember

Question 1

The thermistor is made of semiconductor material
Using band theory, explain why the conductivity of the thermistor increases as it is heated

Answer 1

The band gap between the valence and the conduction band in semiconductors is small
Giving electrons heat energy allows more per second to jump from the valence band to the conduction band

Question 2

Light from sun is used to produce a visible spectrum
A student views this spectrum and observes a number of dark lines as shown
Explain how these dark lines in the spectrum of sunlight are produced

Answer 2

photons of particular/some/
certain energies/frequencies are
absorbed (1)
in its/the Sun’s (upper/outer)
atmosphere/outer layers (1)

Question 3

Emission lines occur

Answer 3

at specific wavelengths which relate to the electron energy transitions

Question 4

Explain how emission spectrum is then produced from this atom

Answer 4

Sometimes when electrons drop energy levels, photons are given off. The photons wavelength is dependent on band gap energy levels
This generates a spectra and each line represents the wavelength of a photon

Question 5

Magnetic fields are used to contain plasma inside the fusion reactor.
Explain why it is necessary to use a magnetic field to contain the plasma

Answer 5

Plasma would cool down if it came too close to the sides and reaction would stop

Question 6

Why is energy released in fusion/fission?

Answer 6

Mass is converted into energy

Question 7

Explain in terms of waves how a maximum is produced

Answer 7

Peaks meet in phase

Question 8

Using band theory, explain how a potential difference is produced when photons of light are incident on the photodiode

Answer 8

Electrons gain/absorb energy from
photons/light (1)
Electrons move from valence band to
conduction band (1)
Electrons move towards n-type
semiconductor (producing a
potential difference). (1)

Question 9

Particle composed of quark-antiquark pair

Answer 9

Meson

Question 10

Pions have a mean lifetime of 26ns in their frame of reference
Explain why a greater number of pions are detected at the second detector than would be expected if relativistic effects are not taken into amount

Answer 10

For a stationary observer’s frame of
reference, the mean lifetime of the
pion is greater (than 26 ns)
OR
In a pion’s frame of reference, the
distance is shorter (than 30.0 m).

Question 11

Explain why protons are accelerated by an electric field

Answer 11

Protons are (positively) charged (1)
Protons experience a force (in the
electric field) (1)

Question 12

The train emits a beam of light towards the stationary observer
State the speed of the emitted light as measured by the stationary observer
Justify your answer

Answer 12

3x10^8
Speed of light is the same for all observers

Question 13

Explain, in terms of energy band gaps, the difference between photons emitted by the red LEDs and photons emitted by the blue LEDs

Answer 13

The (energy) band gap in a blue LED
is greater. (1)
The photons of blue light have more
energy (than the photons of red
light). (1)

Question 14

Why is an alternating voltage used in the cyclotron

Answer 14

To ensure electric field is always acting in correct direction

Question 15

Describe an experiment to verify the inverse square law for a point source of light

Answer 15

Place the light detector a distance from the lamp. Measure the distance from the light detector to the lamp and the irradiance of the light at this distance. Repeat these measurements for different distances between detector and lamp. Plot a graph of light irradiance against 1/distance2 from the lamp.

Question 16

One feature of the Bohr model of the hydrogen atom is that the electron can only occupy discrete energy levels
State one other feature of the Bohr model of the hydrogen atom

Answer 16

A (central) positively charged
nucleus.
OR
When an electron moves from one
state to another, the energy lost or
gained is done so ONLY in very
specific amounts of energy.
OR
Each line in a spectrum is produced
when an electron moves from one
energy level/orbit/shell to another.

Do not accept:
Atom is mainly empty space.
Nucleus is small compared to size of
atom.
Any statement referring to photons
and photon frequency is a
consequence, not a feature.

Question 17

Explain how a line emission spectrum is produced

Answer 17

If an electron is in an excited state it
can return to a lower energy level.
When it does this, it emits a photon.
(1)
Different transitions produce
different lines/ frequencies (of
photons).

Question 18

Explain why some lines on a line emission spectrum are brighter than others

Answer 18

(For the brighter lines) more
electrons are making those
transitions (per second).
(1)
(Therefore), there are more photons
(per second) emitted (of that
specific energy and so produce
brighter lines).

Question 19

Explain why protons are accelerated by an electric field

Answer 19

Protons are (positively) charged (1)
Protons experience a force (in the
electric field) (1)

Question 20

The student observes a second yellow spectral line at a wavelength of 589.6 nm
The student observes that the line at 589 nm is brighter than the line at 589/6 nm
Explain this observation

Answer 20

There are more electrons (per
second) making the transition for the
589.0 nm line. (1)
Meaning more photons (per second)
are emitted. (1)
OR
There are fewer electrons (per
second) making the transition for the
589.6 nm line. (1)
Meaning fewer photons (per second)
are emitted. (1)

Question 21

Describe how this apparatus could be used to verify the inverse square law for a point source of light

Answer 21

Obtain values of irradiance for different distances (1)
Plot graph of I against 1/d^2
(1)
Graph of I against 1/d^2 is a straight line through the origin (then this verifies the inverse square law of
light) (1)

Question 22

Explain why the reading on the voltmeter decreases when the switch is closed

Answer 22

Now current in circuit
So voltage can be lost to internal resistance

Question 23

Describe a method to obtain an accurate value for the period T using only a stopwatch

Answer 23

Measure the total time over a
number of swings (1)
Divide total time by number of
swings (1)

Question 24

Suggest an improvement to the experimental procedure that would allow a more previse value for the minimum period T to be determined

Answer 24

Use smaller increments around the
‘turning point’.
OR
Take more measurements about the
‘turning point’.
OR
Take more measurements over the
whole range.

Question 25

State one way in which the experiment could be improved for calculating irradiance
Justify your answer

Answer 25

Smaller lamp
Will be more like a point source

Question 26

Explain why a spectrum is produced in the glass prism

Answer 26

 Different frequencies/ colours
have different refractive indices
(1)
or
 Different frequencies/
colours are refracted through
different angles (1)

Question 27

Suggest why connecting wires in a circuit would have a large diameter

Answer 27

(Wire of large diameter) has a low
resistance (1)
or
to prevent overheating (1)
or
to prevent wires melting (1)

Question 28

Explain why charging current decreases as battery charges

Answer 28

The e.m.f. of the battery
increases (1)
Difference between the two e.m.f.s decreases (1)

Question 29

Using the same apparatus, the student now wishes to determine more precisely the minimum angle of deviation
Suggest two improvements to the experimental procedure that would achieve this

Answer 29

Repeat measurements (1)
More measurements around/ close
to a minimum or smaller ‘steps’ in angle (1)

Question 30

Why is energy released in a fusion reaction

Answer 30

Mass is converted into energy

Question 31

One student states that the clocks on board the plane will run slower when plane is travelling at relativistic speeds
Explain whether or not this statement is correct

Answer 31

Correct – from the perspective of
the stationary observer there will be time dilation

Question 32

A voltage is applied across an LED so that it is forward biased and emits light
Using band theory, explain how the LED emits light

Answer 32

(Voltage applied causes) electrons
to move towards conduction band of
p-type/ away from n-type (towards
the junction) (1)
Electrons move/ drop from
conduction band to valence band
(1)
Photon emitted (when electron
drops) (1)