4.3 Electrical Circuits

Question 1

What is Kirchhoff’s second law?

Answer 1

For any path (loop) of a circuit, the sum of all of the potential differences must equal to total emf of the circuit

Question 2

How do you find the total resistance in a series circuit?

Answer 2

R(total) = R(1) + R(2) + R(3) +…

Question 3

How do you find the total resistance in a parallel circuit?

Answer 3

1/R(total) = 1/R(1) + 1/R(2) + 1/R(3) +….

R(total)⁻¹ = R(1)⁻¹ + R(2)⁻¹ + R(3)⁻¹ +…

Question 4

True or false:

Adding a resistor to a circuit in parallel will always reduce the total resistance

Answer 4

True

Total resistance drops the more paths there are for the current to take

Question 5

How can you measure the current in a circuit?

Answer 5

You can measure the current in a circuit with an ammeter connected in series with the component

Question 6

How do you measure potential difference of a component?

Answer 6

Using a voltmeter, connected in parallel over the component being measured

Question 7

True or false:

In parallel circuits the total voltage in each loop is the same

Answer 7

True

V(total) = V(1) = V(2) = V(3)

Question 8

How do you calculate the total voltage in series circuits?

Answer 8

V(total) = V(1) + V(2) + V(3) +…

Question 9

How does the current vary between each component of a series circuit?

Answer 9

The current through all of the components is the same so the current does not vary

Question 10

Is the current in each component of a parallel circuit the same

Answer 10

No each branch of a parallel circuit has different currents
Because the voltage across each branch is the same - the higher the resistance of a branch, the lower the current flow through that branch will be

Question 11

If you connect two cells in series what will be the total emf?

Answer 11

e(total) = e(1) + e(2)

Question 12

In a series circuit, if two cells are connected negative to negative, would their emf add up or cancel out?

Answer 12

They will cancel out. The total emf would be equal to:

e(total) = e(1) - e(2)

Question 13

True or false:

The emf of a source and its terminal voltage will always be the same

Answer 13

False

Not all of the energy given to the charges in the source (emf) makes it out of the cell

Question 14

Define internal resistance

Answer 14

Internal resistance is the resistance within a power source due to the materials and components which make it up

Question 15

What are ‘lost volts’?

Answer 15

Lost volts refer to the difference in voltage between that supplied by the source and the amount available to the circuit

They are lost due to the internal resistance of the source

Question 16

Give an equation which relates emf to load and internal resistance

Answer 16

ℰ = I(R+r)

ℰ = IR +Ir

Question 17

Describe an experiment to determine the internal resistance of a source

Answer 17

• Set up a circuit with a source, ammeter and variable resistor in series and a voltmeter in parallel
• Vary the resistance and. measure the voltage and current
• Plot a V-I graph
• V= -rl + ℰ corresponds to. y=mx+c
• the internal resistance = -m

Question 18

what is the purpose of a potential divider?

Answer 18

To provide variable potential difference or to provide a constant specific potential difference

Question 19

How does the voltage across a component in a potential divider correspond to its resistance?

Answer 19

The proportion of the total voltage which is dropped across the component is equal to the proportion of the circuit resistance which it contributes
In other words: V/V(T) = R/R(T)

Question 20

What equation can be used to calculate the voltage out of a potential divider in terms of the input voltage and the resistance in the circuit?

Answer 20

V(out) = (R(out)/R(total) x V(in)