Question 22M.2.SL.TZ1.c.ii
| Date | May 2022 | Marks available | [Maximum mark: 2] | Reference code | 22M.2.SL.TZ1.c.ii |
| Level | SL | Paper | 2 | Time zone | TZ1 |
| Command term | Outline | Question number | c.ii | Adapted from | N/A |
A power supply is connected to three resistors P, Q and R of fixed value and to an ideal voltmeter. A variable resistor S, formed from a solid cylinder of conducting putty, is also connected in the circuit. Conducting putty is a material that can be moulded so that the resistance of S can be changed by re-shaping it.
The resistance values of P, Q and R are 40 Ω, 16 Ω and 60 Ω respectively. The emf of the power supply is 6.0 V and its internal resistance is negligible.
All the putty is reshaped into a solid cylinder that is four times longer than the original length.
Outline, without calculation, the change in the total power dissipated in Q and the new cylinder after it has been reshaped.
[2]
«total» power has decreased ✓
Because current in the branch has decreased «and P=I2R »
OR
Because resistance has increased in branch «and » ✓
Allow opposite argument as ECF from (c)(i) (if candidate deduces a lower resistance).
Allow “power doesn’t change” if candidate has no change of resistance from (b) to (c)(i).
This was an item that caused a bit of confusion for candidates. The prompt asks for a comparison of the power in the branch before and after changing the length of the conductive putty. Many candidates correctly identified that the power in Q would decrease, but either did not discuss the power in the whole branch or were not clear that the power in the putty would decrease as well.
