Basic Concepts and Resistance

Question 1

Movement of charge is

Answer 1

an electrical current

Question 2

Charge of a electron and proton

Answer 2

+- 1.6x10-19C

Question 3

Unit of charge

Answer 3

C

Question 4

If a battery is rated at 120 amp hours it is

Answer 4

able to provide flow of 120 amps for one hour - way of describing charge as Q =It

Question 5

E=

Answer 5

VQ=VIt= energy in J

Question 6

P=

Answer 6

Power in watts W, It=Et = I^2 R = VI = V^2 /R

Recommend to use I^2 *R

Question 7

kWh

Answer 7

Unit of power 1kWh is equal to power of 1000W being delivered for a period of 1 hour

Question 8

Which side of a cell diagram is positive

Answer 8

longer slide current leaves the longer side and returns to the shorter side

Question 9

What is an ideal voltage supply

Answer 9

Delivers a prescribed voltage across its terminals independent of the current flowing through it, no internal resistance

Question 10

What is an ideal current supply

Answer 10

Delivers a prescribed current through its terminals independent of the voltage across them

Question 11

A resistance is an

Answer 11

energy sink, converts electrical energy into thermal energy

Question 12

Ohms Law

Answer 12

V=IR

Question 13

Calculating the resistance of a material

Answer 13

R = rho * L/A where rho is resitivity in ohms per metre

Question 14

What is conductivity

Answer 14

conductivity is the reciprocal of the resitivity ie 1/rho

it has unit siemens per metre S/m and given symbol sigma

Question 15

What is conductance

Answer 15

conductance is 1/R it has symbol G units siemens S or ohms to the minus 1

Question 16

How does resistance vary with temperature

Answer 16

as you increase temperature resistance increases

Question 17

What is Ro

Answer 17

Resistance of a material at 0 degrees Celsius

Question 18

If after several hours the current has reached a certain point what does this mean

Answer 18

The temperature has gotten to a steady point as the heat generated due to the resistance is equal to the heat lost to the surroundings

Question 19

When using P=VI or P=V^2R

Answer 19

make sure that you are using voltage across the resistor of interest equation does not work otherwise

Question 20

In series how do you add resistance

Answer 20

simply some Rt=R1 + R2 + R3 +….

Question 21

At a node what is the rule for current

Answer 21

a node is a join, what goes in must come out current in = current out

Question 22

in parallel how do you add resistance

Answer 22

1/Rt=1/R1 + 1/R2 + 1/R3 + ….

Question 23

What is internal resistance

Answer 23

Resistance of a battery (will be in series)

Question 24

what is the open circuit or no load voltage

Answer 24

When you have a non ideal battery it is the voltage supplied by the battery before the internal resistance
it would be the voltage across the terminal if no voltage was connnected

Question 25

When does maximum power output occur and what does this mean

Answer 25

RL=Rint (load resistance) = (internal resistance), that maximum possible efficiency is 50% as equal power dissipation, can greater efficiency at lower power ouputs

Question 26

Prove that max power output occurs at RL = Rint

Answer 26

setup basic internal resistance circuit with load resistance calculate current flowing through circuit Calculate the power going to the load resistor differentiate with respect to the load resistance and equate to zero

Question 27

Whats the difference between an ideal and a practical current source

Answer 27

a practical source will have an internal resistance parallel to it

Question 28

Where does the waste power go in a practical voltage supply

Answer 28

it heats up the source

Question 29

maximum power output to any load occurs when

Answer 29

its resistance is equal to that of the rest of the circuit