6.19.M - Lesson: Using Electricity

Amperes

Amperes are standard unit for the strength of an electric current.

Electricity

Electricity is the movement of charged atomic particles called electrons.

current = voltage / resistance

(formula for current)

Comparison of series circuit on top and parallel circuit on bottom.

(image of a series circuit on top and parallel circuit on bottom)

Consider a simple circuit with an outlet, a switch, and a 60 watt light bulb. If the switch is closed, the light operates. When a second 60-watt bulb is added to the circuit in parallel with the first bulb, it is connected so that there is a path to flow through to the first bulb or a path to flow through to the second bulb. Both bulbs glow at their intended brightness since they each receive the full circuit voltage of 120 volts, which is the average voltage of an electrical wall socket.

(image of lamp) and (image of electric socket)

Electricity is a form of energy involving the flow of electrons. When electrons move, they carry electrical energy from one place to another. This is called current electricity or an electric current. Electric currents are also involved in powering all the electrical appliances you use, including the refrigerator, television, and toaster.

(image of lightbulbs)

A battery is a chemical device designed to create the force needed to move electrons. Conductors are usually metals like copper, that provide a path for electrons to flow. Electrons have a negative charge. They travel out of the negative terminal (-) and are attracted to the positive terminal (+). Touch a metal conductor to each end of the battery and electrons begin to flow from negative to positive. Never connect a short wire from the negative terminal to the positive terminal of a battery. This creates a short circuit. The wire will get really hot and you could burn yourself. Also, the battery quickly loses energy.

(image of many batteries)

One example of a series circuit is a string of old Christmas lights. When one bulb in the strand goes out, the entire strand of lights quit working.

(image of old Christmas lights)

An advantage of parallel circuits is that the burnout or removal of one bulb does not affect the other bulbs in parallel circuits. They continue to operate because there is still a separate, independent closed path from the source to each of the other loads. That's why parallel circuits are used for wiring lighting and receptacle outlets. If one light on a parallel circuit burns out, it is the only one that quits and the other lights wired in parallel stay lit.

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Consider a simple series circuit consisting of a 120-volt outlet as the source, a switch, and a 60 watt light bulb. When the switch is open, the light cannot operate since the circuit is not complete. There is no closed-loop path for the current to flow through the circuit. When the switch is closed, the light bulb operates since the current flows through the circuit. The bulb glows at its full brightness since it receives its full 120 volts and has the design current flow. If two light bulbs are connected to the circuit in series, the resistance of the circuit doubles. The current flow is now half of what it was when only one lamp was in the circuit as before. The voltage across each lamp is now 60 volts due to the reduced current flow. Each bulb is operating at only one-half of its intended voltage, which will reduce its brightness.

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Electricity is a type of energy that can build up in one place or flow from one place to another. Electricity that gathers in one place is known as static electricity, and electricity that moves from one place to another is called current electricity.

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Flowing electrons are called current. Current is measured in amperes. The force moving the electrons is voltage and is measured in volts. The path the electric current flows is called a circuit.

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Volts and Amperes

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What is the current produced by a 12-volt battery connected to a circuit with a resistance of 25 ohms?

.48 A

If a 12-volt battery produces a current of 25 amperes, what is the resistance?

.48 ohms

An electric heater works by passing a current of 100 A through a coiled metal wire, making it red hot. If the resistance of the wire is 1.1 ohms, what voltage must be applied to it?

110 V

Battery

A battery is a chemical device designed to create the force needed to move electrons.

Circuit

A circuit is a path on which an electric current flows.

Conductor

A conductor is something that provides a path on which electrons can flow.

Parallel

A parallel circuit is a circuit in which there are at least two independent paths in the circuit to get back to the source. In a parallel circuit, the current will flow through the closed paths and not through the open paths. Looking at the schematic diagram, we see that points 1, 2, 3, and 4 are all electrically common. So are points 8, 7, 6, and 5. Note that all resistors, as well as the battery, are connected between these two sets of points. In a purely parallel circuit, there are never more than two sets of electrically common points, no matter how many components are connected. There are many paths for current flow, but only one voltage across all components.

Short Circuit

A short circuit is an excessive flow of electric current that may result in blowing a fuse, tripping a breaker, or starting a fire.

Current

Current is flowing electrons.

Current

Current is the rate that electrons are flowing. It is measured in amperes, which is often abbreviated to amps. Electrons are very tiny. One amp means that 6,250,000,000,000,000,000 electrons flow through the circuit per second. One amp is the current flowing through a typical flashlight.

Electricity

If you've ever sat watching a thunderstorm, with lightning bolts darting down from the sky, you'll have some idea of the power of electricity. A bolt of lightning is a sudden, massive surge of electricity between the sky and the ground beneath. The energy in a single lightning bolt is enough to light 100 powerful lamps for a whole day!

Ohm's Law

Ohm's Law explains the relationship among voltage (pushing), current (being pushed), and resistance (resisting the current being pushed or slowing it down). Ohm discovered that the amount of current in a circuit is directly proportional to the voltage across the circuit and inversely proportional to the resistance of the circuit. Below is the formula:

Example 2 If an electric skillet draws the current of 15 A and is connected to a 120 V circuit, what is the amount of resistance in that circuit? In this example, we are given the current and voltage. We plug in the numbers and solve for resistance. 15 A = 120 V / x Multiply both sides by x: 15x = 120 V Divide both sides by the current: x = 120 V / 15 A

The amount of resistance in the electric skillet circuit is 8 Ω or 8 ohms. 120 V/15A = 8 Ω

Series

The basic idea of a "series" connection is that components are connected end-to-end in a line to form a single path through which current can flow. In this circuit, the current flows in a clockwise direction, from point 1 to point 2 to point 3 to point 4, and back around to 1. This means all of the currents in the circuit must flow through all of the loads. Opening or breaking a series circuit at any point in its path causes the entire circuit to "open" or stop operating. That's because the basic requirement for the circuit to operate is a continuous, closed-loop path, which is no longer met. This is the main disadvantage of a series circuit. If any one of the light bulbs or loads burns out or is removed, the entire circuit stops operating.

So ohms measure resistance in an electric circuit. The job of any resistor is to slow down amperage. Knowing the resistance and how to control it makes electricity safer to use. The voltage pushes amperage or current through resistors. If you understand the concept, then the math will come easier.

The symbol for ohms looks like a horseshoe (Ω).

Series vs Parallel Circuits

There are two basic ways in which to connect more than two circuit components: series and parallel. Understanding the difference between a series circuit and a parallel circuit can really improve your mood when you are decorating your Christmas tree.

Practice Problems

Try these practice problems. You will need to remember these formulas for your lesson review.

Voltage

Voltage is the measure of the force moving the electrons that is measured in volts.

Voltage

You look at a battery and find the voltage. For example, if you look at an AA battery, you will find either the word volts or a V preceded by a number. In the picture, you can see the voltage of this AA battery is 1.5 V. Volts is a measure of the force moving the electrons. It is safe to touch a AA battery because the voltage is too low to shock you.

Example 1 If you wanted to know how much current flows through a light bulb with a resistance of 60 Ω when the current was impressed by 12 volts, what would you do? Just plug in the numbers and divide the voltage by the ohms.

You will divide the voltage (12 volts) by the resistance 60 ohms). This will give you the total current, which is .2 Amps. 0.2 A = 12 volts/60 Ω

The far left image shows a circuit that contains a battery, a light bulb, and wires (conductors). To move electricity through the bulb, we complete the circuit by touching the metal wire to each end of the battery. The electric current flows from the negative terminal (-) to the positive terminal (+) of the battery. The wire doesn't get hot because the light bulb reduces the current flowing in this circuit. Electric energy converts to light energy.

[image of circuit that contains a battery, a light bulb, and wires (conductors)]

In units, it is expressed like this:

amperes = volts/ohms