E.m.f And Internal Resistance Flashcards
Internal resistance makes what
BATTERIES and CELLS warm up
What does resistance come from
ELECTRONS colliding with ATOMS and losing ENERGY
Why does batteries warm up
Use CHEMICAL energy to make ELECTRONS move
As they move, they COLLIDE with atoms inside the BATTERY
So resistance must have resistance- this is called internal resistance
How does the chemical energy make he electrons move
Chemical reactions in the battery produce electrical energy
What is load resistance also known as
External resistance
What is load/external resistance
The TOTAL RESISTANCE of ALL the COMPONENTS in the EXTERNAL circuit
What is e.m.f
The AMOUNT of ELECTRICAL ENERGY
PRODUCED by the BATTERY
for each COULOMB of CHARGE
Isn’t actually a force-measures in volts
What does e.m.f stand for
Electromotive force
What is the potential difference across you load resistance
The ENERGY TRANSFERRED
when ONE COULOMB of CHRAGE
flows through the LOAD RESISTANCE
If there is no internal resistance what should we notice about the terminal p.d and the e.m.f
Should be the same
What is the potential difference across the load resistance called
Terminal p.d
What is lost volts
The ENERGY WASTED
PER COULOMB
OVERCOMING
the INTERNAL RESISTANCE
What does the conservation of energy tell us
Energy per coulomb SUPPLIED by the SOURCE = energy per coulomb USED in LOAD resistance + energy per coulomb WASTED in INTERNAL resistance
What are the symbols of each: Load/external resistance Terminal p.d Internal resistance Electromotive force Lost volts
R V r e v
We are given this equation
V=e-Ir
What can we sub in to change it to make another one
V=IR
v=Ir
What need low internal resistance
Powerful supplies
Why does a car battery need to have a low internal resistance
As it has to DELIVER a really high CURRENT
What are also the same
CELLS used to POWER a torch or a personal stereo
Generally batteries have an internal resistance of what
Less than 1 ohm
Since internal resistance caused energy loss, what would you think
All POWER SUPPLIES should have a LOW INTERNAL RESISTANCE
What are the exception
HIGH VOLTAGE POWER SUPPLIES
Name some high voltage power supplies which are designed with a very high internal resistance
HT (high tension)
EHT (extremely high tension)
Why do high voltage power supplies have a very high internal resistance
If they are accidentally SHORT-CIRCUITED
only a VERY SMALL CURRENT can flow
-SAFER
How would you use a circuit to measure internal resistance and e.m.f
Changing value of R (load resistance) measuring I and V Plot graph of V against I Use equation V=e-Ir rearrange to V=-rI+e Gradient is -r (V/I) Y intercept is e
What is an easier way to measure the e.m.f of a power source
Connecting a HIGH-RESISTANCE VOLT ETER across its terminals
A SMALL CURRENT FLOWS through the VOLTMETER
So there must be some LOST VOLTS
Means you measure value SLIGHTLY LESS THAN the e.m.f
