Electricity

Question 1

What ideal resistance should ammeters have

Answer 1

No resistance
Reduces effect on current

Question 2

What ideal resistance should voltmeters have

Answer 2

Infinite resistance
No current passes through it

Question 3

Conventional current

Answer 3

Positive to negative

Question 4

Difference between electrolyte (ionic solution) and current

Answer 4

Charge carriers are e
Charge carriers are ions

Charge carriers are -
Charge carriers + or -

Question 5

Similarity between electrolyte (ionic solution) and current

Answer 5

Both are flows of charge

Question 6

K’s 1st law

Answer 6

Due to conservation of charge.
In electrical circuit sum of current into a point/junction is equal to sum of current out of that point/junction

Question 7

Mean drift velocity

Answer 7

Average velocity of electron passing through object

(Proportional to current, Inversely proportional to charge carriers and area)

Question 8

EMF

Answer 8

• Energy per unit charge supplied by a source
• Work done on charge carriers
• Energy transformed to electrical

Question 9

Define Pd

Answer 9

• Work done by the charge carriers as they move through the component
• Energy transferred from electrical to another form
• Charges loses energy

Question 10

Explain the meaning of internal resistance

Answer 10

Some energy transferred into thermal energy/ lost as heat in the battery

Question 11

Why does resistance increase with temp

Answer 11

Positive ions in wire have more internal energy
Ions vibrate more
Higher frequency of collions between charge carriers and ions
Charge carriers do more work / transfer more energy

Question 12

Resistance and resistivity

Answer 12

Resistance- measure of how difficult it is for current to flow

Resistivity- measure of how difficult it is for charge to flow
Conductors have low resistivity
Insulators have high resistivity

Question 13

Explain lost V in terms of distance of wire

Answer 13

• As d increases R of wire and load resistor increases
~ gets bigger share of emf
• I decreases so less emf lost inside battery
• due to internal resistance

Question 14

K’s 2nd law

Answer 14

Due to conservation of energy. Sum of pd in closed loop equal to sum of emf

Question 15

LED IV characteristics

Answer 15

Non ohmic component
Resistance very high when its polarity doesn’t allow current to pass through
As pd increases resistive starts to decrease
Eventually resistance drops a lot for small increase in pd
Small R

Question 16

Thermistor and uses

Answer 16

As temp increases, resistance decreases
Thermostats (control heating)
Kettles (measure temp)
Monitor engines (prevents over heating)

Question 17

Thermistor IV characteristics ( why does R de as T in)

Answer 17

Non ohmic
Number density of charge carriers increase
Current increases
Resistance decreases

Question 18

LDR

Answer 18

As light intensity increases, resistance decreases
When light shines, number density increases

Question 19

What’s kilowatt hour

Answer 19

Energy transferred with power of one kilowatt for one hour

Question 20

How does capacitor plates A & B get oppositely charged

Answer 20

e move clockwise/anticlockwise
e deposited at plate connected to negative terminal
e removed from plate connected to positive terminal giving it a positive charge