Current, Voltage & Power

Question 1

What are electrical circuits

Answer 1

A circuit consists of electrical or electronic components interconnected with metal wires.

Question 2

What is electrical charge

Answer 2

Charge is an electrical property possessed by some atomic particles.

Question 3

What is charge measured in

Answer 3

Charge is measured in Coulombs (abbreviated C)

Question 4

What is the charge of an electron

Answer 4

−1.6 × 10−19 C

Question 5

What is the charge of a proton

Answer 5

+1.6 × 10−19 C

Question 6

What is a current

Answer 6

Current is the flow of charged particles past a measurement boundary.

Question 7

What is current measured in

Answer 7

Using an ammeter, we measure current in Ampères (usually abbreviated to
Amps or A)

Question 8

What is the equation for current

Answer 8

I (A) = Q (C) / T (s)

Question 9

What does potential energy difference does not depend on

Answer 9

• on the route taken between the points
• on your choice of reference surface (e.g., lake surface or sea level)

Question 10

What is a node in a circuit

Answer 10

All the points that are connected via the interconnecting wires

Question 11

What is the assumptions of nodes

Answer 11

Interconnecting wires have zero resistance so everywhere along a node has the same voltage.

Question 12

What is the electrical potential difference (or voltage difference) between any two nodes in a circuit

Answer 12

The energy per coulomb needed to move a small +ve charge from one node to the the other

Question 13

What is a resistor

Answer 13

A thin strip of metal film deposited onto an insulating ceramic base and is the link between current and voltage

Question 14

How is voltage and current related

Answer 14

Graph

Question 15

What direction is current and voltage choose in

Answer 15

Opposite direction

Question 16

For a resistor what can we calculate

Answer 16

• Resistance
• Conductance

Question 17

What is the relationship between current and voltage

Answer 17

Directly proportional

Question 18

Resistance Equation

Answer 18

R = V/I

Question 19

What resistance measured in

Answer 19

Ohms (Ω)

Question 20

Conductance Equation

Answer 20

G = 1/R = I/V

Question 21

What is conductance measured in

Answer 21

Siemens (S)

Question 22

Describe the flow of current in a resistor

Answer 22

Flows from a high voltage (more positive) to a low voltage (more negative)

Question 23

What happens when current flow through a resistor

Answer 23

The electrical potential energy that is lost is transformed into heat

Question 24

Resistor Power Dissipation

Answer 24

The power dissipated as heat in a resistor is equal to V × I Watts (W). 1 Watt equals one Joule of energy per second

Question 25

What sign is power dissipation is and why

Answer 25

Since V and I always have the same sign (see graph) the power dissipation is always positive

Question 26

Ideal Voltage Source

Answer 26

Has a constant voltage value no matter how much current is flowing from it

Question 27

Ideal Current Source

Answer 27

Provides a fixed amount of current no matter what the voltage is across the source.

Question 28

If the source is supplying electrical energy to a circuit

Answer 28

VI < 0

Question 29

When a rechargeable battery is charging

Answer 29

VI > 0

Question 30

Sum of all power in a circuit

Answer 30

0