Question 22N.2.HL.TZ0.9
| Date | November 2022 | Marks available | [Maximum mark: 10] | Reference code | 22N.2.HL.TZ0.9 |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Calculate, Describe, Determine, Draw, Explain, State | Question number | 9 | Adapted from | N/A |
A parallel-plate capacitor of capacitance 1.5 × 10−10 F is made from two metal plates separated by an air gap of 1.0 mm. The capacitor is initially charged to a potential difference of 24 V.
Calculate the energy stored in the capacitor.
[1]
«» «J» ✓
A very well answered question.
The charged capacitor is disconnected from the voltage supply and the separation between the plates is increased to 4.0 mm.
Explain the change, if any, to the potential difference between the plates.
[2]
«from » capacitance decreases «by factor 4 / to 3.8 × 10−11 F» ✓
«from » charge unchanged hence p.d. increases by factor 4 / to 96 «V» ✓
Award [1] max for a reasoning without numbers.
A well answered question though often lacking numerical detail.
Determine the work required to increase the separation of the plates.
[2]
work = (energy in the new arrangement) − (initial energy) ✓
«energy increased by factor 4 hence» work = 3 × 4.3 × 10−8 =1.3 × 10−7 «J» ✓
Allow ECF from 9(a).
Award [2] for a BCA.
Different strategies were observed here, some successful, some including a choice of wrong formulae.
The capacitor is then discharged through a fixed resistor. The initial current in the resistor is and the time constant of the circuit is .
Draw, on the axes, a graph to show the variation with time of the current in the resistor.
[2]
exponential decrease from current = I0 ✓
approximately correct values for time = AND 2 ✓
For MP2, the curve should be between 0.30 and 0.45 when time t = and below 0.20 when time t = 2.
The general shape of the curve was usually correct. Many candidates scored full marks, but the most common mistakes were ones that fell to 0.5 after one time constant, as if there was an attempt to identify a particular value, or fell far too steeply if not.
A similar mathematical relationship can be used to model phenomena in other areas of physics.
State an example of such a phenomenon.
[1]
«activity vs time in» radioactive decay
OR
thermal energy transfer ✓
Accept any other appropriate physics phenomenon, as X-ray absorption.
Accept terminal velocity as the question can be interpreted as a phenomenon modelled with an exponential function (i.e. including growth).
Do not accept dice throwing.
A high scoring question with most choosing radioactive decay. Some lost the mark by identifying wave phenomena or just an incomplete reference to half-life.
A diode bridge rectification circuit is often modified by adding a capacitor in parallel with the output (load) resistance.
Describe the reason for this modification.
[2]
without a capacitor, output voltage/current drops to zero «twice per cycle of input voltage» ✓
capacitor provides smoothing / smooths out voltage/current variations ✓
voltage/current output becomes constant / similar to direct current output ✓
voltage/current does not drop to zero ✓
by returning some of its energy/charge to the circuit «when input voltage is low» ✓
Generally, candidates either made a good job of this, suggesting a number of credit worthy points or had no idea and guessed something to do with resistances/capacitances in parallel.