Electrical Circuits

Question 1

What are the rules for series circuits?

Answer 1

Current is the same.
Total voltage is the sum of all.
Total resistance is the sum of all.

Question 2

What are the rules for parallel circuits?

Answer 2

Total current adds up.
Voltage is same.
Total resistance is equal to less than the resistor with the smallest resistance.

Question 3

If there are two branches in a parallel circuit, one with half the resistance than the other, how is the total current distributed?

Answer 3

The one with half resistance will have double the current, so this branch has 2/3 of the total current

Question 4

What is Kirchhoff’s first law?

Answer 4

Conservation of charge. The sum of the currents entering a junction is equal to the sum of the current leaving the junction.

Question 5

What is Kirchhoff’s second law?

Answer 5

Conservation of energy.
The sum of the elctromotive forces are equal to the sum of the pds around a closed loop.

Question 6

How can we show Kirchhoff’s first and second law in a numerical way

Answer 6

Check notes

Question 7

What does adding additional components in series do to pd?

Answer 7

Reduces the potential difference that is hsared between the origional components.

Question 8

Use Kirchhoff’s laws to explain the rules in series circuits.

Answer 8

1st law - single loop so current equal
2nd law - Sum of pd across all components equals to emf

Question 9

Use Kirchhoff’s laws to expalin rules in parallel circuits

Answer 9

1st law - current in each branch different so add.
2nd law - each branch is closed loop so pd equal in each loop.

Question 10

Explain resistors in series.

Answer 10

Vt = v1 + v2 + …. since V=IR
IRt = IR1 + IR2 + …. Since I is constant
Rt = R1 + R2 + ….

Question 11

Explain resistors in parallel.

Answer 11

It = I1 + I2 + …. Since Vt = V1 = V2
It/Vt = I1/v + I2/v + ….
1/Rt = 1/R1 + 1/R2 + ….

Question 12

How to get resistance from 1/R?

Answer 12

Reciprocal answer

Question 13

What are resistor circuits?

Answer 13

Difference combinations of resistors in series and parallel.

Question 14

Why does internal resistance matter when choosing a cell?

Answer 14

More interal resistance decrease current (more safe). Less (large current for motors)

Question 15

Where does internal resistance come from in chemical and solar cells?

Answer 15

Chemical reactions, resistance of materials in cells.

Question 16

What must happen for charges to get through cell?

Answer 16

Work done

Question 17

How are lost volts made?

Answer 17

Some energy is lost as work is done known as lost volts.

Question 18

What is left over from lost volts to form the total e.m.f?

Answer 18

Terminal pd (across the cells)

Question 19

How does terminal pd change when current decreases?

Answer 19

Less charges travel, less work done, less lost volts, more terminal pd.

Question 20

Formula for emf.

Answer 20

e.m.f = terminal pd + lost volts so
e.m.f = terminal pd + IR so
E = IR + IR so
E = I(R + r)

Question 21

What is the formula for lost volts?

Answer 21

Lost volts = current * internal resistance