physics 2020 paper 1

Question 1

An electrician replaced the switch.
The electrician would have received an electric shock unless the circuit was
disconnected from the mains supply.
Explain why.

Answer 1

one wire in the switch is live
the electrician is earthed
or
the electrician is at earth
potential
(so) there will be a (large)
potential difference between the
live wire and the electrician /
earth (if the electrician touched
the wire

Question 2

Explain why adding resistors in parallel decreases the total resistance.

Answer 2

multiple paths for charge /
electrons to flow
total current is greater (for the
same potential difference when
more resistors are added)

Question 3

The student concluded that the number of resistors in parallel was inversely
proportional to the mean total resistance.
Explain why the student was correct.
Use data from Figure 12 in your answer

Answer 3

two pairs of values of n and R
showing that n × R = constant
third pair of values of n and R
showing that n × R = constant
(so) n × R = constant (showing
the student was correct

Question 4

precise

Answer 4

precise results show little
variation
the 4th result was further away
from the mean than the other
values

Question 5

At the bottom of the slide, all riders and their sleds have approximately the same
speed.
Explain why.

Answer 5

½ mv2 = mgh
or
decrease in Ep = increase in Ek
masses cancel on both sides of
the equation
or
v2 = 2gh
(final) speed only depends on
vertical height (and gravitational
field strength)
variations will be due to air
resistance/friction
or
different initial speed

Question 6

Explain the advantage of the radioactive waste having a shorter half-life

Answer 6

activity decreases quickly
risk of harm decreases quickly

Question 7

Explain how the process of nuclear fusion leads to the release of energy

Answer 7

lighter nuclei join to form heavier
nuclei
some of the mass (of the nuclei)
is converted to energy (of
radiation

Question 8

Nuclear fission releases energy.
Describe the process of nuclear fission inside a nuclear reactor.

Answer 8

neutron absorbed by a uranium
nucleus
nucleus splits into two parts
and (2 / 3) neutrons (are
released)
and gamma rays (are emitted)

Question 9

When replaced, the cells were put into the torch the wrong way around.
Explain why the torch did not work.

Answer 9

there is no current in a diode (in
the reverse direction)
or
charge will not flow through a
diode (in the reverse direction)
(because) a diode has a (very)
high resistance (in the reverse
direction)

Question 10

What is meant by a zero error?

Answer 10

ammeter displays a reading
when not connected (to a circuit