Chapter 10 - Electric Circuits

Question 1

Define the equation and units for current

Answer 1

Current (i) = Q / t
Q = charge, t = time
SI unit of current is ampheres and coulombs / sec o volts / ohm
Current is the flow of positive charge

Question 2

What happens to current as magnitude and velocity increase and electrons accelerate?

Answer 2

Current increases proportional to magnitude, velocity and acceleration of electrons

Question 3

State Ohms Law (voltage)

Answer 3

V = I x R or R = V^2 / P
where I is current and R is resistance. Resistance must remain constant

Voltage can also equal the electric field strength times the distance between plates
V = E x d

Question 4

State the equation for resistance R

Answer 4

R = (r x l) / A
where r is resistivity, l is length and A is cross-sectional area.
Resistance increases with temp bc more collisions.
Electrical resistance increases with temp, density and length
Also
R = V^2 / P
P can be power or work

Question 5

How does voltage decrease from positive flow affect energy?

Answer 5

Energy loss from positive flow

Vq = Vlt = joules

Question 6

Define the equation for power loss (voltage)

Answer 6

(V x L x t) / t = Vi = watts

= V^2/R = i^2/r

Question 7

Provide the equation for terminal voltage

Answer 7

Vt = V - (i x r)
Vt = IRt
Where V is max voltage

Question 8

Explain the role of current at a junction and the effect of direction on potential

Answer 8

Current arrives at junction positive, and leaves junction negative. Positive current in a clockwise direction increases potential. Negative current goes in an anticlockwise direction and decreases potential.

Question 9

Define capacitance and its equation

Answer 9

C = charge / voltage = Q / V
SI unit is the farad, also coulomb / volt. Capacitance is proportional to surface area and inversely proportional to distance between plates
C = Q /E x d

Question 10

If potential difference to a resistance is doubled, how much power is dissipated?

Answer 10

Power = V^2 / R
Where if R doubles, V will quadruple
Also
Power = i x V

Question 11

How does increases the voltage across 2 plates of a capacitor affect charge?

Answer 11

Charge = capacitance x voltage

Increasing voltage therefore increases charge

Question 12

What is the effect of increasing capacitance to area distance and voltage?

Answer 12

Increase capacitance causes decreased voltage. Increasing area, decreasing distance between plates will also cause increased capacitance.
Increase dielectrics, increases capacitance

Question 13

Resistors in parallel have…

Answer 13

Resistors in parallel have the same voltage and the same current throughout them

Question 14

What is the equation for power

Answer 14

Power = i x v
Power = V^2 / R
Also Power = I^2R
since squared, current increases exponentially

Question 15

What is the resistance able to generate 200 w and 120 V

Answer 15

Ohm’s Law R = V^2 / P
120^2 = 14400 V / 200w
= 72 ohms (omega)

Question 16

An appliance generates 200 watts of power, it runs for 3 hours, how much energy is used?

Answer 16

Work = power x time (time always in seconds)
work = 200W x 3 hours x 60 minutes x 60 seconds
Work = 200 W x 10800s
Work = 2.2 x 10^6 J

Question 17

What is the correct arrangement for a circuit

Answer 17

Voltometer in parallel with resistor and ammeter in series

Question 18

Maximum voltage is 1000v, what is the power if the current is 50amp

Answer 18

Power = i x V
Power = 50 x 1000 = 50 000 W = 50 kW

Question 19

Find resistance if voltage is 1000 and and current is 50

Answer 19

V = i x R so R = V / i
R = 1000 / 50 = 20