Electrical Principles & Random Misc Practice Questions

Which of the following is not cause of electricity?

• heat

• magnetism

• pressure

• inertia

• chemicals

Answer explanation

There are six ways that atoms can give up or “free” their electrons?

1. Heat ------ called thermoelectricity     

2. Magnetism ----- called electromagnetism

3. Friction ------ called triboelectricity

4. Pressure ------ called piezoelectricity

5. Chemicals ------ called chemoelectricity

6. Light ------ called photoelectricity Inertia is defines as resistance to motion or change.     

If the voltage is kept constant at 240 volts, and the resistance measures 40 ohms, the current flowing through the conductor is:

• 6 amps

• 60 amps

• 24 volts

• 240 volts

• 6 volts

Answer explanation

When the source of EMF provides a constant potential difference in the circuit and the temperature is constant, current is inversely proportional to resistance; when resistance goes up, current goes down; when resistance goes down, current goes up.

The three forms of Ohm’s Law follow:

1.      R = E             I

2.      E = I x R

3.      I = E           R                                                                            

Where R is the resistance in ohms, E is the applied emf in volts, and I is the current in amperes.

Relays are made up of a __________ and one or more __________.

• switch, loads

• source, switches

• transformer, loads

• load, switches

• load, transformers

Answer explanation

The relay is composed of two devices: 1. The coil portion, which is a load and performs work (the action of physically moving a switch). 2. A switch that controls the power source to another load.

A battery is an example of a/an ____________ source.

• alternating current

• series current

• magnetic

• parallel circuit

• direct current

Answer explanation

Direct current flows constantly in one direction. A battery is one source of direct current. It will always have two poles or terminals, one negative (-) and one positive (+). The electron flow is from positive to negative inside the battery. However, the external flow for the electrical circuits is always negative to positive. The electrons flow in only one direction. Direct current will continue to flow until the circuit is broken or the source of energy stops supplying electrons.

“VA” is the common term for:

• amps

• ohms

• watts

• volts

• gigajoules

Answer explanation

Electrical power relates to the time rate of doing work. The definition of electrical wattage is 1 watt of power is used to perform work when 1 volt causes 1 ampere of current flow for 1 second. The letter P is used to represent electrical power. Power is measured in units of the watt. The formula for electric power is:  

         P = E x I

Transformers are Rated in Volt - Amps

Transformer Rating = VA

VA = Voltage x Amperage

Example: VA = 24 Volts x 2 amps, VA = 48VA

The 120V side of the transformer found on most heating system is referred to as the:

• primary winding

• secondary winding

• hot winding

• initial winding

• number one winding

Answer explanation

Transformers are available in a variety of capacities for stepping-up or stepping down AC voltages.

The construction of a step-down transformer is simple. Windings of insulated wire and placed around one side of an iron core. This winding is connected to the power source and is called the primary winding. Another separate winding of insulated wire is placed opposite of the core. This is called the secondary winding.

There is no physical electrical connection between the primary and secondary of the transformer. Electrical energy is transferred from primary windings to secondary windings by the process of induction.

“Current flowing through a conductor in one direction for a split second, then in the opposite direction for a split second” would be a good definition of:

• alternating current

• direct current

• voltage

• resistance

• wattage

Answer explanation

Alternating current is defined as current flowing through a conductor in one direction for a split second, then in the opposite direction for a split second.

Materials which do not allow their electrons to spin out of orbit easily are called:

• conductors

• grounds

• insulators

• elements

• magnets

Answer explanation

To produce electromagnetism, either the conductor moves through the field or the field is moved across the conductor. All that is really required is relative motion between a conductor and a magnetic filed.

The device which operates similar to a fuse, but which can be reused, is a:

• switch

• circuit breaker

• load

• source

• conductor

Answer explanation

There are two major types of circuit protectors, fuses and circuit breakers.

A fuse is used in a circuit to protect the wiring against overloads. An overload occurs whenever there is too much current for the size of the wire. This could happen if too many loads are plugged into the same circuit.

The other type of circuit protector is the circuit breaker. Some circuit breakers look much like a switch. They usually have a lever with an ON and OFF position.When in the ON position, current flows through a thermal device within the breaker. If excessive current passes through this device, it heats up. If the thermal element gets too hot, it trips the breaker. When the breaker is tripped, the lever is in the OFF position and the circuit is open. After the thermal element has cooled sufficiently, the breaker can be manually reset to close the circuit again.

Another type of circuit breaker looks like a regular strip fuse with a button protruding from the top. When this breaker trips, it can be manually reset by pressing the button.

The rate of flow of electrons in a circuit is termed:

• voltage

• amperage

• resistance

• induction

• wattage

Answer explanation

The ampere is the unit which represents the flow of electrons in an electrical circuit used to measure the flow of electrons in an electrical circuit.