E.m.f And Internal Resistance Flashcards Preview

Physics Section 3: Current Electricity > E.m.f And Internal Resistance > Flashcards

Flashcards in E.m.f And Internal Resistance Deck (25)
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0

What does resistance come from

ELECTRONS colliding with ATOMS and losing ENERGY

1

Internal resistance makes what

BATTERIES and CELLS warm up

2

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

3

How does the chemical energy make he electrons move

Chemical reactions in the battery produce electrical energy

4

What is load resistance also known as

External resistance

5

What is load/external resistance

The TOTAL RESISTANCE of ALL the COMPONENTS in the EXTERNAL circuit

6

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

7

What does e.m.f stand for

Electromotive force

8

What is the potential difference across you load resistance

The ENERGY TRANSFERRED
when ONE COULOMB of CHRAGE
flows through the LOAD RESISTANCE

9

If there is no internal resistance what should we notice about the terminal p.d and the e.m.f

Should be the same

10

What is the potential difference across the load resistance called

Terminal p.d

11

What is lost volts

The ENERGY WASTED
PER COULOMB
OVERCOMING
the INTERNAL RESISTANCE

12

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

13

What are the symbols of each:
Load/external resistance
Terminal p.d
Internal resistance
Electromotive force
Lost volts

R
V
r
e
v

14

We are given this equation
V=e-Ir
What can we sub in to change it to make another one

V=IR
v=Ir

15

What need low internal resistance

Powerful supplies

16

Why does a car battery need to have a low internal resistance

As it has to DELIVER a really high CURRENT

17

What are also the same

CELLS used to POWER a torch or a personal stereo

18

Generally batteries have an internal resistance of what

Less than 1 ohm

19

Since internal resistance caused energy loss, what would you think

All POWER SUPPLIES should have a LOW INTERNAL RESISTANCE

20

What are the exception

HIGH VOLTAGE POWER SUPPLIES

21

Name some high voltage power supplies which are designed with a very high internal resistance

HT (high tension)
EHT (extremely high tension)

22

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

23

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

24

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