ESAT · Physics
ESAT physics scaling questions
Work out how one quantity changes when others are scaled, without needing the actual values.
How to spot it
- What is the ratio ...?
- By what factor does ... change?
- What is the new value as a percentage of the old?
Try one
Original example
Two wires are made of the same metal. Wire Q is twice as long as wire P and has twice the diameter.
What is the resistance of Q divided by the resistance of P?
The method
- Write the formula linking the quantities.
- Write new over old, so constants cancel.
- Put in the scale factors and simplify.
The trap
Watch forScaling with the diameter as if area were proportional to it, or forgetting a square.
Now a harder one
Harder
A heater has a fixed resistance. The voltage across it is reduced by 10%.
By what percentage does the power of the heater fall?