Chapter 10- Electrical Circuits

Question 1

Kirchhoff’s 2nd Law

Answer 1

In any circuit, the sum of the electromotive forces is equal to the sum of the potential differences in a closed loop

Question 2

Closed loop

Answer 2

A series circuit or one branch of a parallel circuit

Question 3

Series circuit rules

Answer 3

The current is the same everywhere

The potential difference is split between the components directly proportional to the resistance

Question 4

Parallel circuit rules

Answer 4

Current is split between the loops inversely proportional to the resistance of each
Potential difference of each branch is equal to the emf of the power supply

Question 5

If one loop has a resistor on it and another one doesn’t:

Answer 5

All the current flows through the loop without a resistor

Question 6

Resistance in series

Answer 6

The total resistance is equal to the sum of the resistances of each individual resistor

Question 7

Resistance in parallel

Answer 7

The inverse of the total resistance is equal to the sum of the inverses of the resistances of each path

Question 8

Terminal p.d.

Answer 8

The potential difference where some of the energy is “lost” as heat in the power supply - the p.d. that gets used in the rest of the circuit

Question 9

Lost volts

Answer 9

The difference between the emf and the terminal p.d.

Question 10

Internal resistance

Answer 10

The resistance of the power supply due to the chemicals in the cell it can be effectively drawn as a resistor in the cell
Represented by r

Question 11

Using e.m.f = terminal p.d. + lost volts

Answer 11

ε = V + Ir
ε = IR + Ir
ε = I(R+r)

Question 12

Relationship between e.m.f. and p.d. at low currents

Answer 12

ε ≈ V

Question 13

Cells in series

Answer 13

The total e.m.f. is the sum of each

Higher internal resistance so limited current

Question 14

Cells in parallel

Answer 14

The e.m.f. is that of one cell

Lower internal resistance so higher current

Question 15

Internal resistance as a graph

Answer 15

V = -rI + ε

In the form y = mx + c

Question 16

What is a potential divider circuit

Answer 16

It splits the potential difference to give any required value up to the maximum provided by the power supply

Question 17

Potential divider circuit makeup

Answer 17

It has two resistors, R1 and R2. R2 has the p.d. required by the component and the component is placed in parallel around that resistor,

Question 18

Potential divider circuit ratios

Answer 18

V1/V2 = R1/R2

Question 19

Potential divider circuit equation

Answer 19

( R2 )
Vout = ( ————) x Vin
( R1 + R2 )

Question 20

Loading a potential divider circuit

Answer 20

Putting a component with resistance parallel to R2 will decrease the resistance for that part of the circuit, lowering Vout

Question 21

Effects of loading with different resistances

Answer 21

Loading with a large resistance has little effect on Vout but loading with a small resistance massively decreases it

Question 22

Using a variable resistor as R2 in a potential divider circuit

Answer 22

Allows you to vary the output p.d.

Increasing the resistance increases the output p.d.

Question 23

LDR in a potential divider circuit

Answer 23

As R2, increased light intensity decreases resistance and decreases output p.d.
As R1, increased light intensity decreases resistance and decreases p.d. around R1, increasing R2

Question 24

Thermistor in a potential divider circuit

Answer 24

As R2, increased temperature decreases resistance and decreases output p.d.
As R1, temperature decreases resistance and decreases p.d. around R1, increasing R2

Question 25

Potentiometer

Answer 25

Made of a sliding contact which you can move between 3 terminals. Moving it towards A increases V out until it equals V in and moving towards B decreases it until it equals 0.

Question 26

Potentiometer advantages

Answer 26

Compact
Output p.d. ranges from 0 to Vin
Made of less components

Question 27

What causes a light to light up?

Answer 27

The current