Chapter 8.1 - Current & Charge

Question 1

What is current measured in

Answer 1

Amperes (A) [I]

1 A (SI unit) = 1Cs^-1 (C/s) (charge is derived from current and time)

Question 2

Current and Charge equation

Answer 2

I =🔺Q /🔺t

🔺Q = I🔺t

Question 3

Charge definition

Answer 3

• Charge is a physical property
• 2 types of charge (+ / -)
• like repel
• opposites attract

Question 4

Current definition

Answer 4

• Rate of flow of charge

* Amount of charge passing a given point in a circuit per unit time

Question 5

What is charge measured in

Answer 5

• Coulomb (Q) [C]
• Equivalent to 1 A s (ampere x second)
• Relative charge

Question 6

Elementary charge

Answer 6

1.60 x 10^-19 C

Charge of one proton [e]

Relative charge of one proton is +1e
Relative charge of one electron is -1e

Question 7

Net charge definition

Answer 7

• Size of charge on object is multiple of e
• Result of add or removal of electrons
• Q = +- n e
• Q - net charge of object in coulombs
• n - number of electrons
• e - elementary charge

Question 8

Quantised definition

Answer 8

Describe charge on object as quantised

Charge must be integer multiples of e

Question 9

Describe Millikan’s experiment - discovery of quantisation of charge

Answer 9

• Analysed the motion of electrically charged oil droplets between two oppositely charged parallel plates
• Oil droplets experienced gravitational force, air resistance, and upthrust

• Occasionally oil droplets were stationary in the air
-gravitational force was balanced by upward electrostatic force

• Other droplets drifted slowly through electric field
• Millikan found that the charge on any droplets was quantised of e
• Determined e was -1.59 X 10^-19