Power and Circuit Protection in Series and Parallel Circuits

Question 1

Describe how Ohm’s law is used to calculate
values of an electrical circuit

Answer 1

V=I*R
I=V/R and R=V/I
Voltage equals Current times Resistance

Question 2

Describe how Krichhoff’s law is used for the
calculation of values in an electrical circuit

Answer 2

Kirchhoff’s voltage law states that the total change in voltage around any closes loop in a circuit is zero. The sum of the voltage drops across a line of series resistors will equal the supplied voltage.

VT=V1+V2+V3+ …
The voltage of the circuit (Power Supply) equals the sum of the individual drops.

Question 3

Define power and give its units of measurement

Answer 3

Power is the time rate of energy transfer. I’m electrical systems it is the time rate of energy consumed by the circuit. It’s unit is the Watt (W)

Question 4

State a formula for calculating the total power
used in an electrical circuit

Answer 4

P= I*V
Or P= I squared *R
In a series circuit: PT= P1+ P2+ P3+…

Question 5

State Kirchhoff’s Current Law and give an application

Answer 5

Kirchhoff’s current law states that the sum of the current flows into and out of any node in a circuits is equal to zero.
Application: calculate the equivalent resistance for two parallel resistors in order to determine the main line current in a circuit.

Question 6

State a formula for calculating total parallel resistance

Answer 6

The formula for calculating the total resistance (Rt) of resistors in parallel is 1/Rt = 1/R1 + 1/R2 + 1/R3 + ….

Question 7

Describe the function of two types of circuit
protection and give an application of each

Answer 7

Fuse- high Current melts the metal inside the fuse, breaking electrical contact. Used in automotive electrical systems.

Question 8

Describe the operation of a fuse and give its
schematic symbol

Answer 8

A fuse consists of a piece of wire made of a metal or an alloy of an appropriate melting point, for example, aluminum, copper, iron, lead etc. If a current larger than the specified value flows through the circuit, the temperature of the fuse wire increases. This melts the fuse wire and breaks the circuit.

Question 9

Describe the operation of two types of circuit
breakers and give their schematic symbols

Answer 9

Circuit breakers can be either thermally or magnetically triggered.

Question 10

Calculate series resistance given each load’s resistance

Question 11

Use Ohm’s Law to calculate voltage, current, and
resistance in a series circuit

Answer 11

VT=I*RT (Total voltage equals the main line current times the total resistance)

I=V/RT (Current equals voltage divided by total total resistance)

R=V/I (Resistance equals voltage divided by current)

Question 12

Calculate the total power used by a series circuit

Answer 12

PT= P1+P2+P3+…
PT= I*V
PT= I squared *R

Question 13

Calculate the main line current in a parallel circuit

Answer 13

First calculate the equivalent resistance
RT= 1/( 1/R1+ 1/R2+ 1/R3+…)
Then, calculate the main line current
I= V/RT

Question 14

Calculate the total parallel resistance

Answer 14

You can find total resistance in a Parallel circuit with the following formula: 1/Rt = 1/R1 + 1/R2 + 1/R3 +…

Question 15

Calculate the total power used in a parallel circuit

Answer 15

To figure out the total power used by a parallel circuit, you have to multiply the voltage of the battery by the current flowing out of the battery. To figure out the power used by a particular branch, you have to multiply the voltage used by the branch by the current flowing through it