The Student Room Group

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2. the current I in a conductor of cross-sectional area A is given by the formula: I = nAQv, where Q is the charge on the charge carrier.
a. state the means of n and v.
n: charge carrier density
v: average velocity


c. two pices of wire A and B are made of the same material but have different diameters. they are connected in series with each other and a power supply.
i. which terms from the above equation will be the same for both wires?
??

4. a cell of emf E and internal resistance r is connected in a circuit with a resistor of resistance R. the current in the circuit is I.
a. using the symbols in the diagram write down a formula for:
i. the rate of conversion of chemical energy in the cell
ii. the power dissipated in the resistor of resistance R
iii. the power dissipated in r.
b. use these formulae to write an equation based on conservation of energy in the circuit.

5. an electric drill shown below is labelled 230V, 200W. it has a removable steel drill bit that is used to drill into a wall for 30s.
a. calculate how much electrical energy is used by the drill during this time
230 V x 200 W x 30
= 1380000J


b. after use the steel drill bit is very hot. the mass of the drill bit is 15g. the room temp is 20 degrees cels. Calculate the max possible temp of the drill bit. State an assumption you have made.
SHC of steel = 510 J kg-1 K-1

c. the actual temp of the drill bit will be less than this. suggest a reason why.

THAAAAANKYOU SO MUCH
Reply 1
2c) the only thing that has changed is the diameter, so only A changes (i guess that means current would too, dunno if it means both sides)

5a) you don't need to consider voltage - it give you a power, and a time, multiply them.

b) you know the energy transferred. divide it by the SHC and the mass (in kg). this would be the change in temp caused. to find the final temp add it to the room temp at the start.

c) some heat transferred to surroundings

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