Question 18M.2.HL.TZ1.7
| Date | May 2018 | Marks available | [Maximum mark: 11] | Reference code | 18M.2.HL.TZ1.7 |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Calculate, Describe, Determine, Explain | Question number | 7 | Adapted from | N/A |
A capacitor consists of two parallel square plates separated by a vacuum. The plates are 2.5 cm × 2.5 cm squares. The capacitance of the capacitor is 4.3 pF.
Calculate the distance between the plates.
[1]
d = « =» 1.3 × 10–3 «m»
[1 mark]
The capacitor is connected to a 16 V cell as shown.
Calculate the magnitude and the sign of the charge on plate A when the capacitor is fully charged.
[2]
6.9 × 10–11 «C»
negative charge/sign
[2 marks]
The capacitor is fully charged and the space between the plates is then filled with a dielectric of permittivity ε = 3.0ε0.
Explain whether the magnitude of the charge on plate A increases, decreases or stays constant.
[2]
charge increases
because capacitance increases AND pd remains the same.
[2 marks]
In a different circuit, a transformer is connected to an alternating current (ac) supply.
The transformer has 100 turns in the primary coil and 1200 turns in the secondary coil. The peak value of the voltage of the ac supply is 220 V. Determine the root mean square (rms) value of the output voltage.
[3]
ALTERNATIVE 1
εs = × 220
= 2640 «V»
Vrms = = 1870 «V»
ALTERNATIVE 2
(Primary) Vrms = = 156 «V»
(Secondary) Vrms =
Vrms = 1870 «V»
Allow ECF from MP1 and MP2.
Award [2] max for 12.96 V (reversing Np and Ns).
[3 marks]
Describe the use of transformers in electrical power distribution.
[3]
step-up transformers increase voltage/step-down transformers decrease voltage
(step-up transformers increase voltage) from plants to transmission lines / (step-down transformers decrease voltage) from transmission lines to final utilizers
this decreases current (in transmission lines)
to minimize energy/power losses in transmission
[3 marks]