Chapter 10 - Electrical Circuits

Question 1

What is kirchofff’s second law?

Answer 1

In any circuit the sum of the e.m.f.s is equal to the sum of the p.d in a closed loop

Question 2

How do kirchoff’s laws work in a series circuit?

Answer 2

Current is the same all the way around
Charge is the same
Emf = sum of p.d. across components
Emf is shared equally if resistance in components is equal
Otherwise component with greater resistance takes greater proportion of emf
If there is more than one source of emf you add them all up

Question 3

How do kirchoff’s laws work in a parallel circuit?

Answer 3

More resistance in branch = less current through it (half resistance = double current)
In a branch sum of p.d. of components must equal emf of source

Question 4

What happens when you add more resistors in series?

Answer 4

Resistance increases

Total resistance = r1 + r2 + ….

Question 5

What happens when you add more resistors in parallel?

Answer 5

Resistance decreases

1/Total resistance = 1/r1 +1/r2 + …

Question 6

What are the 4 key electrical relationships?

Answer 6

I = change in charge / change in time

V = W/Q

P=IV P=I^”R

V=IR

Question 7

What is internal resistance?

Answer 7

When there is current work has to be done so some energy is lost and not all of it is available to be used

We call these lost volts

Question 8

How does current affect internal resistance and p.d.?

Answer 8

As current increases, the emf does not change but the terminal p.d. drops as lost volts increase

Question 9

What is the relationship with emf, lost volts and terminal p.d.?

Answer 9

Emf = terminal p.d. + lost volts
Emf = V + Ir
So
Emf = IR + Ir (R = resistance in circuit) (r is internal resistance of power supply)

Emf = I(R+r)

Question 10

What happens to terminal p.d. When R=infinity or 0?

Answer 10

When R = Infinity
V = Emf
When R = 0
V = 0