Topics 9 + 10: electricity and dc circuits

Question 1

Define current

Answer 1

Charge flow per unit charge

Question 2

What is the formula relating current and charge?

Answer 2

I = Q / t

Question 3

What does everything stand for in I = nAqv and what is each part measured in?

Answer 3

I - current (A)
n - charge carrier density (m^-3)
A - cross-sectional area of conductor (m^2)
q - charge on carrier (c)
v - drift speed (ms^-1)

Question 4

Define potential difference across a component

Answer 4

energy transferred for unit charge

Question 5

What is the formula relating work done to voltage?

Answer 5

V = W / Q

Question 6

Define emf

Answer 6

energy transformed into electrical energy per unit charge (in a power source)

Question 7

Define resistance

Answer 7

Potential difference divided by current

Question 8

What is Ohm’s law?

Answer 8

current is directly proportional to potential difference (when temperature is the same)

Question 9

What are the 3 formulas for electrical power?

Answer 9

P = VI
P = I^2 x R
P = V^2 x R

Question 10

What formula contains resistance and resistivity?

Answer 10

R = ρL/A

Question 11

What is Kirchhoff’s first law?

Answer 11

The total current entering a junction is equal to the total current leaving that same junction

Question 12

What is Kirchhoff’s second law?

Answer 12

The sum of emfs is equal to the sum of potential drops in a closed loop