Internal Resistance Flashcards
if the conservation of electrical charge and energy is true, does that mean that all of the chemical energy in the cell of a circuit that is converted into electrical energy should emerge at the other terminal of the cell
- no
- the electrical energy returning to the cell is less than the chemical energy that is originally converted
if not, where is the energy being used instead
- to push the electrons through the cell
- this reduces the overall magnitude of the electrical energy coming back to the cell compared to the initial magnitude of the chemical energy
why is some of the energy converted by the cell used up inside the cell first in the first place
- to overcome the resistance it has
- so electrons can flow through
what is the name given to the resistance that the cell has when a current tries to flow through
- the internal resistance of the cell
- given the symbol r
if you had a circuit with a cell, a lamp and a current flowing through, what would be the symbols representing the cell and its resistance, along with the resistance of the lamp
- the cell produces and e.m.f. (e)
- and its internal resistance is labelled r
- the lamp has a normal resistance of R
- while the current is just I
if there is a current in the circuit, what word equation can be written for the rate of energy converted in the cell
rate of energy converted in the cell = rate of work done against internal resistance + rate of work done lighting lamp
what is the symbol equation for it, then simplified
- eI = I^2r + I^2R
- e = Ir + IR
how would you rearrange that simplified equation for V
- IR = e - Ir
- since V = IR
- V = e - Ir
how would you therefore represent the difference between the emf of a cell and the potential difference at its terminals using the equation
e - V = Ir
why does that equation make sense
- some energy is initially used to overcome the internal resistance of the cell
- that means that all of the electromotive force isnt used to produce a pd but instead some is used for the overcoming
- as emf and pd have a cause and effect relationship (where the emf produces the pd and the pd causes the electrons to move)
- that means that the internal resistance is also the difference between the emf and the pd
what is an alternative rearrangement of the energy equation to find the current
- from the one we just derived it would be I = (e - V) / r
- but an alternative one is I = e / (R + r)
why does that equation make sense
- I = V / R
- if you are adding the internal resistance and normal resistance together you get a total resistance of the circuit
- this means that you dont need to take the difference between e and V into consideration
- so you can assume all the chemical energy is converted to electrical energy
- making e your new V in the equation
