IB FA18.2

How to do the assessment:

1. What is the resistance of an Aluminium wire that is 2.59 mm in diameter (10 gauge) and 12.0 m long? The resistivity of Aluminium is 2.65x10^-8 Ωm. (0.0604 Ω)

Just like this one: Resistivity Ex #1

2. A 25.0 m long copper wire (resistivity = 1.68x10^-8 Ωm) has a resistance of 0.127 ohms. What is its diameter? (2.05 mm)

Use the resistivity formula to find the area (A), then find the radius from the area of a circle (pi r²), and then double that to get the diameter

3. A film resistor is made of a thin film of material that is 1.01x10^-8 m thick, 3.50 cm wide, and 15.0 cm long. What is its resistivity if it has a resistance of 221 ohms? (The current flows a distance of 15.0 cm through the film) (52.1x10^-8 Ωm)

Just like this one: Resistivity Ex #3 - only the area is rectangular = just LxW, in this case (0.035 m)x( 1.01x10^-8 m)

4. With what speed do electrons travel down a 0.240 mm diameter copper wire that is carrying 140. mA of current. (n for Cu is 8.50x10²⁸ electrons m^-3) (2.27x10^-4 m/s)

Just like this one: ElectronDrift - The example problem at 3:58 in the video

5. A 85.0 cm long copper (resistivity = 1.68x10^-8 Ωm, n = 8.50x10²⁸ electrons m^-3) wire is 2.10 mm in diameter, and has a potential of 0.0150 V across it. What time does it take an electron to travel the length of the wire? (hint - find R, then I, then v, then t) (1.10x10⁴ s or 3.06 hours)

1. OK - here's what to do. Use the formula with resistivity to calculate the resistance of the wire:

L = 0.85 m, r = 1.05x10^-3 m, resistivity = 1.68x10^-8 Ωm

2. Then find the current in the wire using Ohm's Law: I = V/R

V = 0.0150 V, R = the answer you got in step 1

3. Then use the electron drift formula to find the velocity:

n = n = 8.50x10²⁸ electrons m^-3, r = 1.05x10^-3 m, I = answer you got in step 2, q = e = 1.602x10^-19 C

4. Then find the time using v = x/t or s/t:

s = 0.85, v = answer you got in step 3

Yay

The Instruction for this unit: