electrical sources and internal resistance

Question 1

an electrical cell is made from materials (metal/chemicals etc) and all materials…

Answer 1

have a resistance. The cell must have a resistance itself - internal resistance

Question 2

Any power supply has two parts:

Answer 2

1. a source of electrical energy

2. internal resistance

Question 3

Electromotive Force (E.M.F.) definition

Answer 3

the energy supplied to each coulomb of charge as it passes through the supply

Question 4

when the switch in a circuit is open, the voltmeter will read…

Answer 4

emf because no current is flowing

Question 5

when the switch in a circuit is closed, current will flow through…

Answer 5

the internal resistor and resistor

Question 6

what is the supply’s voltage that is lost to the internal resistance know as

Answer 6

lost volts

Question 7

what are lost volts

Answer 7

the supply’s voltage that is lost to the internal resistance

Question 8

terminal potential difference

Answer 8

the circuit will not be supplied with the voltage that the supply actually provides

Question 9

how to lay out internal resistance questions

Answer 9

R
I
V
ε
r

Question 10

internal resistance equations

Answer 10

ε=Vtpd+Vlost
Vlost=Ir
Vtpd=IR
ε=IR+Ir
ε=I(R+r)

Question 11

internal resistance and emf in y=mx+c

Answer 11

v=-rI+ε

Question 12

measuring emf and lost volts experimentally

Answer 12

• cell connected in a circuit as shown
• current in circuit altered using variable resistor
• voltmeter measures Vtpd
• results produce this graph (kinda like this: )

Question 13

internal resistance from graph

Answer 13

negative of the gradient

Question 14

emf from graph

Answer 14

y-intercept (current=0 so no lost volts)

Question 15

open circuit

Answer 15

no current flowing (open circuit potential of battery/cell is the emf)

Question 16

what happens to lost volts when current increases

Answer 16

also increase because Vlost=Ir and internal resistance does not change. the lost volts are not available at the terminals of the cell so Vtpd falls

Question 17

short circuit value from graph

Answer 17

max current when external resistance is zero (x-intercept)