4.3 - Electrical circuits

Question 1

State Kirchoff’s second law

Answer 1

Sum of the EMFs is equal to the sum of the potential drops around a closed circuit loop

Question 2

What is Kirchoffs second law a consequence of?

Answer 2

Conservation of energy

Question 3

What can we say about the current through components in series?

Answer 3

Same for each component

Question 4

What can we say about the current on different parallel branches?

Answer 4

It depends on the resistance of each branch

Question 5

What can we say about the pd across parallel branches in a circuit?

Answer 5

It is the same for each branch

Question 6

How do you find the total pd across several components in series?

Answer 6

It is equal to the sum of the pds across each component

Question 7

How do you find the total EMF from cells connected in series with the same polarity?

Answer 7

Their EMFs are added

Question 8

How do you find the total EMF from cells connected in series with opposite polarity?

Answer 8

The total EMF is the difference between their EMFs

Question 9

How do you calculate the total resistance of resistors in series?

Answer 9

Sum of the individual resistances

Question 10

What is the total resistance of n identical resistors in series?

Answer 10

n x R

Question 11

What is the total resistance of n identical resistors in parallel?

Answer 11

R/n

Question 12

How do you calculate the resistance of resistors in parallel?

Answer 12

1/RT=1/R1+1/R2…

Question 13

How does the total resistance change when a resistor is added in series?

Answer 13

It always increases

Question 14

How does the total resistance change when a resistor is added in parallel?

Answer 14

It always decreases

Question 15

What is the effect of connecting two identical resistors in parallel?

Answer 15

Resistance is halved

Question 16

What is the effect of connecting two identical resistors in series?

Answer 16

Resistance is doubled

Question 17

What is internal resistance?

Answer 17

The opposition to current created by the charge carriers having to flow through the source of EMF

Question 18

What are the lost volts for a power supply ?

Answer 18

The pd dropped across the internal resistance OR the difference between the EMF and the terminal pd

Question 19

What happens to the terminal pd of a source as the current supplied increases?

Answer 19

It falls due to the increasing lost volts due to internal resistance

Question 20

How do you calculate lost volts for a supply?

Answer 20

Ir where r is the internal resistance

Question 21

What is the relationship between EMF, terminal pd and lost volts?

Answer 21

EMF=terminal pd+lost volts

Question 22

How do you find the internal resistance from a graph of terminal pd against current?

Answer 22

-gradient

Question 23

How do you find the EMF from a graph of terminal pd against current?

Answer 23

y-intercept

Question 24

What is a potential divider?

Answer 24

Two resistors in series with a fixed source of EMF

Question 25

What determines the ratio of the pd across the resistors in a potential divider?

Answer 25

It is equal to the ratio of their resistances

Question 26

How can a light sensor be made?

Answer 26

By creating a potential divider containing an LDR

Question 27

How can a temperature sensor be made?

Answer 27

By creating a potential divider containing a thermistor

Question 28

What is terminal potential difference?

Answer 28

The potential difference measured across the battery/power supply when that battery/power supply is connected by a complete circuit to a load (external) resistance. If there is no internal resistance, the terminal p.d will equal the e.m.f.