Basic Electricity

Question 1

What is Ohm’s Law and what are the 3 formulas used?

Answer 1

Ohm’s Law: Ohm’s law states that the current through a conductor between two points is directly proportional to the voltage across the two points.

Volts (V) = Current (I) x Resistance (R)
Current = Volts / Resistance
Resistance = Volts / Current

V
——
I R

Question 2

What do volts measure, what is the symbol, what is the unit of measure?

Answer 2

Volts measure the potential for current flow.
Volts = v
Volts are measured in volts

Question 3

What does current measure, what is the symbol, what is the unit of measure?

Answer 3

• Current is the movement of electrons down a conductor.
• Current = I or a
• Current is measured in amps (amperes)

Question 4

What does resistance measure, what is the symbol, what is the unit of measure?

Answer 4

• Resistance measures the opposition to current
• Resistance = R or Ω
• Resistance is measure in the Ohm (Ω)

Question 5

What does polarity measure, what is the symbol, what is the unit of measure?

Answer 5

• Polarity measures positivity or negativity of electrons. The pole having more electrons possesses a negative polarity whereas the other end has a positive polarity.
• Polarity (+) or (-)
• Polarity can be measured in volts.

Question 6

What does power measure, what is the symbol, what is the unit of measure?

Answer 6

• Power is measured in Watts

Question 7

What is Kirchhoff’s Laws (2)?

Answer 7

1) Current Law: For any junction in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node.

2) Voltage Law: The directed sum of the voltages around any closed loop is zero.

Question 8

Why is 3 phase AC electricity the industrial standard?

Answer 8

By using three offset AC sign-waves that have the same synchronized frequency and amplitude, you achieve a similar steady delivery of voltage over time that mimics the current of DC power.

Question 9

What direction do electrons flow?

Answer 9

Electrons in electricity flow from the negative pole to the positive pole.

Question 10

Describe the difference between parallel and series circuits.

Answer 10

Parallel circuits have multiple loops
Series circuits have one loop

Question 11

What is electrical current?

Answer 11

Electrical current is the flow of many negative electrons from one positive nucleus to another positive another nucleus along a conductive path.

Question 12

What is electrical voltage?

Answer 12

The greatness of the electrical field’s potential difference when measured between two points in the field.

Question 13

What is electrical resistance?

Answer 13

Electrical resistance is opposition to electrical current flow.

Question 14

In Ohms Law (I=E/R), E represents what measured in what?

Answer 14

“E” represents the VOLTAGE (potential difference) measured by voltmeter in VOLTS units (v).
E = I x R

Question 15

In Ohms Law (I=E/R), “I” represents what measured in what?

Answer 15

“I” represents CURRENT that flows through the electrical device measured by an ammeter in amperes units (AMPS).

Question 16

In Ohms Law (I=E/R), R represents what measured in what?

Answer 16

“R” represents RESISTANCE of the electrical device, measured by an ohmmeter in OHMS units ( Ω ).
R = E / I

Question 17

How do you find the total resistance (R EQ) in a series circuit?
Can you do the same thing in a parallel circuit?

Answer 17

1) A circuts total resistance equals the sum of all the resisters in a series circut.
R EQ = R1 + R2 + R3 + R4 +….+ R n

2) No
R EQ = (R1+R2)/(R1xR2)
Or
1/R EQ = 1/R1 + 1/R2 + 1/R3 + 1/R4 +….+ 1/R n

Question 18

For resisters in a PARALLEL branch connection/s, what is the relationship between resistance and Voltage?

For resisters in a PARALLEL branch connection/s, what is the relationship resistance and Current?

Answer 18

The voltage across each resistor within a parallel combination is exactly the same but the currents flowing through them are not the same as this is determined by their resistance value and Ohms Law.

Voltage of Resistors in Parallel Branches
- Resistors in parallel branches share the same voltage on their terminals.
- If resistors are connected between the same two nodes, the voltage across each resistor is the same, and the resistors are in parallel.
- The voltage drop across all of the resistors in a parallel resistive network is the same.

CURRENT (Amps) in Resistors in Parallel Branches
- Kirchhoff’s Current Laws states that: “the total current leaving a circuit is equal to that entering the circuit – no current is lost“.
- Then parallel resistor networks can also be thought of as “current dividers” because the supply current splits or divides between the various parallel branches.
-
- The total current (I total) entering a parallel resistive circuit is the sum of all the individual currents flowing in all the parallel branches.
- The resistive value of each branch determines the amount of current flowing within that branch.

Question 19

For resisters in a PARALLEL branch connection/s, what is the relationship between resistance and Voltage?

For resisters in a PARALLEL branch connection/s, what is the relationship resistance and Current?

Answer 19

Voltage of Resistors in Series
- The series resistor networks can also be thought of as “voltage dividers”. Total voltage in a series circuit is the sum of all the individual voltages added together.

Current of Resistors in Series
- Resistors in series have a “Common Current” flowing through them. The current that flows through one resistor must also flow through the others as it can only take one path.
- Then the amount of current that flows through a set of resistors in series will be the same at all points in a series resistor network.

Question 20

How many electrons in a single ampere?

Answer 20

6.242x10^18 electrons

One Amp =
One coulomb =
approximately
six quintillion, two hundred and forty-two quadrillion electrons per second
6,242,000,000,000,000,000
or
6.242x10^18

Question 21

How do you set up a scope-meter to find faults?

Answer 21

Use the “Trigger” feature

Question 22

What are the 3 inputs to a DC power supply?

Answer 22

N = Neutral (black)
L = Load (Red, Hot)
Ground (green)

Power Supply AC-DC (24 volts DC out is common voltage)

Question 23

With a Hot-Cold-Hot meter test:
1) What does the Hot check?
2) What does the Cold check?
3) What does the 2nd Hot check?

Answer 23

1) Hot checks - Proves circuit and meter is working
2) Cold checks - Proves circuit is de-energized
3) 2nd Hot checks - Proves meter is still working after cold check

Question 24

How do you measure nominal voltage and/or current?

Answer 24

Schematics will tell you. Read the schematics before you work on a part

Question 25

What are “Farads”?

Answer 25

Farads
Unit of measure for storing electrical charge
“The farad (symbol: F) is the unit of electrical capacitance, the ability of a body to store an electrical charge, in the International System of Units”

Question 26

What is “dielectric”?

Answer 26

Dielectric = electrical insulator
A dielectric separates a positive & negative plate
“In electromagnetism, a dielectric (or dielectric material or dielectric medium) is an electrical insulator that can be polarised by an applied electric field.”