Types of current, resistivity and electricity

Electrical Resistance and Ohms Law

​Types of current

• ​Current flowing in a circuit can take the form of AC or DC current.

• Alternating current (AC) the standard electricity that comes out of power outlets and is defined as a flow of charge that exhibits a periodic change in direction.

• ​Direct current (DC) power,, is a linear electrical current—it moves in a straight line.

  Direct current can come from multiple sources, including batteries, solar cells, fuel cells, and some modified alternators. Many devices, household appliances, especially, such as lamps, washing machines, and refrigerators, all use AC power, which is delivered directly from the power grid via power outlets.

  Today our electricity is still predominantly powered by alternating current, but computers, LEDs, solar cells and electric vehicles all run on DC power.

• ​

​AC vs DC

• All power outlets bring power into buildings in the form of AC, even where the current may need to be immediately converted into DC power. This is because DC is not capable of traveling the same long distances from power plants to buildings that AC is. 

• ​DC primarily comes into play, where a device needs to store power in batteries for future use. Smartphones, laptops, portable generators, torches, outdoor CCTV camera systems… you name it, anything battery-powered relies on storing DC power. When batteries are charged from the mains supply, AC is converted to DC by a rectifier and stored in the battery.

Multiple Choice

Current that reverses direction in a regular pattern is called ____. 

• direct current 
• circuit current
• magnetic current
• alternating current 

Multiple Choice

Current that does NOT reverse direction is called ____. 

• magnetic current
• direct current
• circuit current
• alternating current

Multiple Choice

What type of current is flowing in the circuit ?

• Alternating current

• Direct current

• Both

• None

Multiple Choice

Which type of current is flowing ?

• Alternating current

• Direct current

• Both

• None

Multiple Choice

Alternating current is produced in most power stations.

• True

• False

Multiple Choice

If you needed a long extension cord, how could you decrease the resistance in the cord?

• make the wire in the cord thinner

• make the wire in the cord thicker

Multiple Choice

If you increase the length of a wire then the resistance will.....

• decrease

• increase

• stay the same

Multiple Select

Choose all that apply.

The longer the extension cord,

• the greater the resistance.

• the less resistance.

• the warmer the cord will become in use.

• the more material the electrons have to flow through.

• the less material the electrons have to flow through.

Multiple Choice

In which of the above wires would electrons experience the least amount of resistance as they flowed through the wire?

• black one on the left

• red one in the middle

• black on on the right

Multiple Choice

The unit which resistance is measured is .....

• Volts

• Amps

• Coulombs

• Ohms

​Generators and Electric Motors

• Both are made of magnets and involve electrical source to give electromagnetic induction.

• Generator is a device that transforms MECHNICAL ebnergy into ELECTRICAL energy.

• Ex. ​Used in hydropowerplants to produce electricity as the turbines spn(mechnical) to give electricity that powers homes

• ​An electrical motor is functionally opposite to a generator.

• ​Electric motors produce MECHANCAL enrfgy from ELECTRICAL energy.

• ​Ex. used in fans to cause the blades to spin

Multiple Choice

Which is NOT a distinctive attribute of an electrical generator?

• Electric generator turns mechanical energy into electric energy

• Electric generator turns electric power into mechanical energy.

• It provides electricity

• It is based upon the electromagnetic induction theory

Multiple Choice

Electric motors are devices that convert _____ energy into  _____ energy.

• electrical; mechanical
• mechanical; electrical
• chemical; potential
• mechanical; kinetic

Multiple Choice

In large generators in power plants, ___________ rotate inside a coil of wire to produce an electric current.

• Wind
• Water
• Magnets
• Circuits

Multiple Choice

What energy transformation takes place in an electric fan's motor?

• electrical energy into mechanical energy

• mechanical energy into electrical energy

• alternating current to direct current

• direct current to alternating current

Multiple Choice

If you increase the width of a wire then the resistance will.....

• decrease

• increase

• stay the same

Multiple Choice

Which of the situation below shows how a basic electric motor works?

• The energy contained in the batteries of the vehicle is transformed into wheel rotation.

• Electrical energy converted into blade rotation in the food processor and cut down food.

• Both A and B

• None of these