Capacitors

Question 1

What is a capacitor?

Answer 1

• device designed to store charge
• two parallel metal plates placed near each other
  
  • both conductors
• insulated from each other

Question 2

What happens when the plates are connected to a battery?

Answer 2

• electrons move through the battery and are forced from its negative terminal of the battery to one of the plates
• an equal number of electrons leave the other plate to return to the battery via its positive terminal
• each plate gains an equal and opposite charge
• creates a uniform electric field

Question 3

When charging a capacitor, how can charge be measured?

Answer 3

• Q = It
• record current at different intervals

Question 4

How can pd of capacitor be measured?

Answer 4

• high-resistance voltmeter connected in parallel
• constant current
  
  • use varaible resistor to keep current constant
• either
  
  • use stop watch and measure the voltmeter at measured times
  • use data loggers

Question 5

What is capacitance?

Answer 5

• C
• capacitance of a capacitor is defined as the charge stored per unit pd

Question 6

What are some examples of uses of capacitors?

Answer 6

• back-up power supplies
• pulse-producing circuits

Question 7

What energy is stored in a capacitor? How does it occur?

Answer 7

• electrons a forced onto plates and taken off other
• energy is stored in the capatacitor as electric potential energy
• discharging capacitor releases energy
• = work to force extra charge into capacitor

Question 8

How is energy released?

Answer 8

• as capacitor is discharged, current flows
• this releases the energy stored as potential energy
• only for a brief period of time

Question 9

What is the area under the V against Q graph?

Answer 9

• 0.5 x base x height = area
• = energy stored by capatcitor
• E = 0.5 QV