A1- self test 1 to 8

1. What are tiny particles that matter is made of called?

2. What are elements called that have atoms with electrons that are easily freed?

which of the following contains atoms of more than one type?

which method is most used to produce electrical energy?

Energy can be neither created nor destroyed

What letter represents the unit of electric charge?

What is the unit for current?

if eight coulombs of charge pass a given point in a conductor over a period of four seconds, current is flowing at a rate of how many amperes? 8/4=2

if 1800 joules of work are required to move 4 coulombs of charge from one point to another, then the potential difference between the two points is how many volts?

What is resistance ?

Write out the three equations forms of ohms law

if a circuit had a current flow of 8 A and the resistance is 20, what is the pressure in volts?

if a circuit has a current flow of 5 A and a pressure of 120 V, what is the resistance ?

how much power will a heater produce if it uses 15 A in a 120 v electrical system ? volts x amps or P= E x I

how many amps will flow through a 60 W headlight bulb in a 24 V system? p=E x I

four main types of electrical drawings: 1. pictorial, 2. block diagrams, 3. wiring diagrams 4. schematic diagram

Which type of diagrams are the easiest to understand for someone with no experience in the electrical trade?

one line diagrams uses symbols for the components and block diagram uses only blocks.

list three distinguishing characteristics of one-line diagrams: 1. to represent a clear picture of the main in line components in the system or circuit. 2. one line diagrams commonly show the highest voltage 3. the components are labelled to show their name, type and sometimes even their catalogue.

six sources of EMF are: friction, chemical, pressure, heat, light and magnetism

one coulomb equal to: 6.24*10(18)= 6, 240, 000, 000, 000, 000, 000

List two hazards of electrostatic charge: lighting and fuel handling

Voltage is the driving force of current, it is the electromotive force which pushes free electrons from one atom to another in the same direction.

electric power is the rate at which work is done or energy is transformed into an electrical circuit.

The current flowing in an electric circuit is directly proportional to the applied voltage an inversely proportional to the resistance of the circuit.

the power in a circuit equals the product of the voltage and the current in the circuit.

Wiring diagram shows as clearly as possible, the actual location of all the components of a circuit

When two wires across, a dot is used to indicate that the wires are connected

If a dot is not shown, the wires across each other but do not connect electrically

The schematic diagram shows electrical relationship between the components of a circuit

The term circuit refers to a circular journey or loop. In the case of an electric circuit, it is the journey or loop travelled by the electrons. Therefore, three basic conditions must exist to have a complete circuit so that electron may flow, for example: source , load and conductor.

Three basic conditions must exist to have a complete circuit so that electron may flow, for example, source, load and conductor.

Short-circuit: A short circuit is simply a low resistance connection between the two conductors supplying electrical power to any circuit.

Open circuit: A circuit in which the continuity is broken due to which the electric current can not flow

closed circuit: A circuit is closed if the circle is complete if all current have a path back to where they came from.

What is provided by a switch in a circuit? Switches control the flow of current through the load by opening the circuit and disconnecting the load from the source.

Why are circuit breakers and fuses added to electrical circuits? Fuses or circuit breakers are added to circuit to protect electrical components from having too much current flow through them. Too much current can cause damage from excess heat, or mechanical damage due to strong magnetic fields.

Which way does current flow from the source out through the load?

1. current flows through loads from negative to positive
2. current flows through sources from positive to negative.

What is the difference between Direct current and Alternating current?

1. Direct current: DC is current that flows in the same direction all the time, for example, batteries, thermocouples, photovoltaic cells, and DC generators. Alternating Current(AC): AC changes its direction continuously and at regular intervals

What are the two common formulas used for determining power dissipation in resistive loads?

1. P=E(2)/R
2. P=I(2)*R

You have a 3000 watt baseboard heater rated for 240 volts, determine the heaters resistance and how much current it draws when operating? R=E(2)/P E=240(2)/ P=3000 57600/3000=19.2 ohms R= 19.2 ohms

A 240 volt electric dryer and the heating element draws 30 amps. Determine wattage the element develops and the resistance of the element? R=E/I 240/30= 8 ohms

you have an electric frying pan rated for 1440 watts at 120 volts. Determine the maximum amps drawn by the electric frying pan and its resistance? R=E(2)/P 120(2)/1440 14400/1440= 10 ohms

You have twelve 120 volt toasters that draw 11 amps each. What is the wattage developed by each toaster? What is the total wattage of all the toasters? What is the resistance of the element of each toaster? R=E/I 120/12=10 10/11=0.909 ohms or 120/11= 10.99 ohms

Seven precautions when handling electrical measuring instruments?

1. Never use a resistance measuring device on a live circuit.
2. measuring resistance , make sure the current is off.
3. voltmeters, ammeters, and watt meters require the circuit power to be on when taking measurements .
4. match the meter to supply, this means that, if you are working with DC, use DC meter and if working with AC, used AC meter.
5. Check that the meter is oriented correctly to be read, some meters are meant to be read with the meter sitting up, and others are meant to be read with the meter lying down.
6. it is important that you read the meter looking straight at the pointer.
7. looking at the meter from off to either side will introduce an error in reading known as parallax error.

List the four things that should be observed when handling watt meters:

1. connect the voltage coil in parallel with the load. Do not exceed the rating of voltage coil.
2. connect the current coil in series with the load. Do not exceed the rating of the current coil.
3. Do not exceed the power rating of the meter.
4. we must observe the polarity of both coils. Otherwise, the meter pointer will try to deflect down below the zero of the scale and meter may be damaged.

What is meant by VOM? Ans: Volt-Ohmmeter (VOM) is a network troubleshooting that measure voltage, amperage and resistance on a cable or other conductive element.

What is a resistor? Ans: A resistor is an electrical component that introduces a specified amount of resistance into a circuit.

How are resistors rated? Ans: Resistor are rated according to their resistance value and their wattage. As the watts rating of a resistor increases, so doe s its physical dimensions. Many of the color-coded resistor also have a tolerance rating.

What are the three main classes of resistors?

There are three main classes of fixed resistors:

1. the wire-wound resistor
2. the film resistor
3. the carbon composition resistor

carbon composition resistor: Red, Brown, Yellow and Gold: Red is 2, Brown is 1 , Yellow is Multiplier of 10 k and gold is +5% Ans: 210kohms+5% ( 210,000+5%)

orange, orange, red and sliver: orange is 3 , orange is 3, red is multiplier of 10k and silver is +10% 330k+10%(33,000 +10%)

yellow, yellow, sliver and gold: yellow is 4, yellow is 4 , silver is multiplier of 0.01 and gold is +5% 0.44ohms+5%

How many terminals does a variable resistor have?

The product of emf, current and time is:

the product of emf and current is :

the product of power and time is:

How many kilowatt hours of energy does it require to operate a 1200 watt hair dryer for 10 minutes? (1200/100=1.2)(10 minutes/60 minutes=0.166666) 1.2*0.1666=

If a 25 kW electric furnace operates for 3 hours in a 24-hour period, and the supply authority charges $ .07/kW/h, what does it cost each day to operate the furnace? (25 kW * 3 h)=75 *.07=5.25

if an electric clothes dryer draws 30 A at 240 V and is operated for 45 minutes, what is the kW/h consumption? (30 A 240 V=7200) 45/60=0.75 M/H 7200/1000=7.2 kW 7.2 kW0.75 h=5.4 kW/h

A 1500 W/240 V baseboard heater is operated for 15 minutes and a 1200 W/120 V baseboard heater is operated for 30 minutes. What is the combined kW/h consumption of the two heaters? At $.07 kW/h, what is the cost of operating the two heaters . solution 1: (1500 W/1000=1.5 kW) (15/60=0.25 kW) 1.5 *0.25=0.375 kW/h solution II: (1200 W/ 1000=1.2 kW)(30/60=0.5 h) 1.2 kW 0.5 h=0.6 kW/h 0.375+0.6=0.975 0.975.07= 0.068

A device that changes electrical energy into other forms of energy is referred to as a

A parallel path of low resistance is the definition of a

Two main types of damage that are likely to occur because of excessively high current are

The term that refers to the charge at one point with respect to another point is

A fuse or circuit breaker protects a circuit from excessive current by ..... the circuit when too much current flows through it.

When a switch is in the open position, is it on or off? Ans: on

current flows through the source from negative to positive

The three necessary components of a circuit are the source, load and conductors

To stop the load, the switch must be open.

If it requires 120 volts to push current through a light bulb at the rate of 2.5 amperes , what is the power rating of the light bulb? and what is the resistance of the filament in the light bulb in the same question?

if a heater connected to a 240 V source of electromotive force draws a current of 3.125 amperes, what is the resistance of the heater ? R=V/I( 240/3.125=76.8 ohms)

if the voltage applied to a circuit increases, the current through the circuit ....

If the resistance of a circuit decreases, the current flowing through the circuit increases

if the resistance of a circuit decreases, the power dissipated by the circuit increases. (power dissipated formular: p=V*I, p=I(2)*R, p=V(2)/R

If the voltage applied to a circuit doubles, the power dissipated by the circuit increases by 4 times .

The current running in an electric circuit is directly related to applied voltage and inversely proportional to the resistance of the circuit

The power in a circuit is equal to the product of the voltage times the current in the circuit

express 13800 volts as kilovolts( 1 kilovolt=1000 volts )

express 500 000 volts as megavolts. ( 1 milliamp=1000 microamperes

express 500 000 volts as megavolts ( 1 million volt= one megavolts ) (500 000/1 000 000)

if the voltage applied to an electric circuit is doubled, what happens to the current flowing through that circuit?

express 18.2 microamperes ( 18.2/ 1 000 000)

Express 470 kilohms as ohms( 470 kilohms *1000)

express 27 000 000 microohms as kilohms( one billions microohms = one kilohms ( 27 000 000/ 1 000 000 000)

How many kilowatts are equal to 1500 watts ? ( 1000 milliwatt= one watt) ( 1500 * 1000=)

express 1500 watts as milliwatts ( 1500 *1000= 1 500 000 milliwatts)

What will happen if you connect a DC meter with wrong polarity?