10.4

Question 1

What is internal resistance

Answer 1

Resistance of emf source (cell/battery) which causes energy/voltage loss as charge passes through source

Question 2

What is terminal pd

Answer 2

• Potential difference across an electrical power source

• If no current then terminal pd = emf

• If current then terminal pd = emf - lost volts

Question 3

What is lost volts

Answer 3

Potential difference across internal resistor of emf source

Question 4

How does changing current affect the terminal pd & lost volts

Answer 4

• Increasing current means more charge travels through cell per second

• More energy is transferred by charges

• Lost volts increases

• Terminal pd decreases

Question 5

What is V = IR applied to internal resistance

Answer 5

• lost volts = I x r (internal resistance)

• If r is fixed
- current is directly proportional to lost volts

Question 6

What is the relationship for emf and lost volts

Answer 6

• emf = terminal pd + lost volts

• If current is very small then emf ≈ pd

• This is why high-resistance digital voltmeter connected in parallel gives reading approximated to be emf

Question 7

What is the relationship for emf from a power source (V = IR but with internal resistance)

Answer 7

• emf = V + lost volts

• emf = V + Ir
-V - terminal pd
-I - current through power supply
-r - internal resistance of power supply

• [V = IR] emf = IR + Ir

• emf = I(R + r)

• Relationship of V = IR using internal resistance of power source