13 Direct current circuits

Question 1

what is the general current rule for junctions?

Answer 1

at any junction in a circuit, the total current leaving the junction is equal to the total current entering the junction

Question 2

what are the current rules for components in series?

Answer 2

• the current entering a component is the same as the current leaving the component
• the current passing through two or more components in series is the same as through each component

Question 3

what is the potential difference rule for components in series?

Answer 3

the total pd across all the components is equal to the sum of the potential differences across each component

Question 4

what is the pd rule for parallel components?

Answer 4

the pd across components in parallel is the same

Question 5

what is the emf rule?

Answer 5

for any complete loop of a circuit, the sum of the emfs round the loop is equal to the sum of the potential drops around the loop

Question 6

what is the rule for resistance in series?

Answer 6

total resistance is equal to the sum of the individual resistances

Question 7

what is the rule for resistance in parallel?

Answer 7

1/R = 1/R1 + 1/R2 etc…

Question 8

what is internal resistance?

Answer 8

the loss of potential difference per unit current in the source when current passes through the source

Question 9

what is emf?

Answer 9

the electrical energy per unit charge produced by the source

Question 10

when is maximum power delivered to a load?

Answer 10

when the load resistance is equal to the internal resistance

Question 11

How do you measure internal resistance?

Answer 11

plot an IV graph of the cell.
gradient is the internal resistance as:
V = E = Ir
r - internal resistance
E - emf

Question 12

what are the characteristics of diodes?

Answer 12

forward direction:
pd = 0.6 V
infinite resistance below 0.6 V
reverse direction:
infinite resistance

Question 13

what is the ratio of pds in a potential divider equal to?

Answer 13

the ratio of the pds across each resistor is equal to the resistance ratio of the two resistors

Question 14

what is a potential divider?

Answer 14

two or more resistors in series with each other and with a source of fixed pd.
the pd of the source is divided between the components

Question 15

what are some uses of potential dividers? - explain how they work

Answer 15

temperature sensor
light sensor