Ch 18 - (Electrical Quantities ) Flashcards
Define current.
- Amount of charge passing a point in a circuit every second
- charge per sec
What is the equation in which change, current and time are related?
Charge = current x time
Q = I x t
Q = charge (coulombs, C)
I = current (amps, A)
What is electric current?
flow of charge
What are the 2 types of current?
- Direct current
- Alternating current
Define direct current.
- electrons flow in one direction only from negative terminal to positive terminal
- produced when using dry cells and batteries
Define alternating current.
- comes from main electricity generators
- direction of electron flow charge changes direction regularly
- typical frequency for the reversal of ac currents, in mains electricity is 50 Hz
How is current measured?
Using ammeters
How should ammeters connected?
In series with part of circuit
What does ammeter do?
- Amount of charge passing through them per unit time
What are the 2 types of ammeters?
- Digital (with an electronic read out)
- Analogue (with a needle and scale )
What is the range of analogue ammeters?
1.0 - 5.0 A
What are the two errors possible for analogue ammeters?
- Zero error
- Parallax error
What do digital ammeters do?
- measure very small currents in mA
- displays accurate values
- easy to use
What are the errors and issues with digital ammeters?
- May flicker
- zero error
How do metals conduct electricity?
flow of electrons
What is the charge of electrons
negative
How do electrons flow?
Negative to positive
How does conventional current flow?
Positive to negative
What is electromotive force?
Name given to potential difference of power source in a circuit
Define electromotive force.
The electrical work done by a source in moving a unit charge around a complete circuit.
What is e.m.f. measured in?
Volts (v)
What is the symbol equation of e.m.f?
E = W / Q
E = electromotive force (V)
W = charged from power source (J)
Q = charge on each carrier (C)
What does potential difference help in?
- light bulb lights up
- related to amount of energy transferred between the 2 points
Define potential difference.
the work done by a unit charge passing through a component
What is the unit of potential difference?
Volts ()V
What is the equation for p.d. ?
V = W / Q
V = potential difference (V)
W = energy from charge carriers (J)
Q = charge on each carrier (C)