4.3 Electrical Circuits

Question 1

What is Kirchoff’s second law?

Answer 1

The total EMF across a circuit loop is equal to the sum of potential differences across devices in that loop

Question 2

What does Kirchoff’s second law conserve?

Answer 2

Energy

Question 3

What happens when cells are added in series? (2)

Answer 3

Current increases

Voltage increases

Question 4

What happens when cells are added in parallel? (3)

Answer 4

Current stays the same
Voltage stays the same
Cells last longer

Question 5

What happens when resistors are added in series? (3)

Answer 5

Voltage stays the same
Current decreases
R = R1 + R2

Question 6

What happens when resistors are added in parallel? (3)

Answer 6

Voltage stays the same
Current increases
1 / R = (1 / R1) + (1 / R2)

Question 7

Value of resistivity - conductors

Answer 7

In the order of 10^-8 ohm metres

Question 8

Value of resistivity - insulator

Answer 8

In the order of 10^16 ohm metres

Question 9

Value of resistivity - semiconductor

Answer 9

10^-8 to 10^16 ohm metres

Question 10

What is internal resistance?

Answer 10

The resistance within a source of EMF, reducing the voltage supplied to the rest of the circuit (r)

Question 11

What are lost volts?

Answer 11

The PD used on the internal resistance

Question 12

What is the internal resistance equation?

Answer 12

E = V + Ir
E: EMF
V: terminal PD (available for use)
Ir: lost volts

Question 13

What are the advantages of using a rheostat in a potential divider circuit? (2)

Answer 13

There is a full range of PD across resistor

Can be used to find IV characteristics

Question 14

How are resistance and voltage divided in a potential divider circuit? (2)

Answer 14

R1:R2 = V1:V2

The PD across each component is proportional to its resistance