Unit 2 ELECTRICITY

Electrostatics is the study Of electrical charges that Can be collected and held in One place.

If the positive charges and the Negative charges balance, an Item is said to be neutral. An insulator is something in Which charge does not move easily. A conductor is something in Which charges move easily through.

Electrical forces must be strong, Because they easily produce Accelerations larger than the One caused by gravity.

There are 4 major rules to Remember about electrical forces: There are two kinds of electrical Charges, positive & negative. Charges exert a force on other Charges over a distance.

The force is stronger when the Charges are closer together. And Like charges repel, opposite Charges attract.

When you charge something by Conduction, you are touching the Object to transfer electrons. When you charge something by Induction, you are just getting A charge close to something To transfer charge.

Electricity did not become an integral Part of our daily lives until Scientists learned to control the Movement of electric charge. This is known as current

Electric currents are responsible For many things; computers, Cars, and every move you make. Current is the rate at which Electric charges move through A given area.

Batteries and generators Supply energy to charge carriers. Both batteries and generators Contain a potential difference (volts) across their terminals. Batteries use chemical energy And generators use mechanical Energy.

Current can be direct or alternating. In Direct Current (DC) the charge Moves only one way through the Wire. (like my electric truck) In Alternating Current (AC), the Charges are constantly changing, Creating no real movement of Electrons. Our house current in the US is 60 Hz.

The SI unit for current is the Ampere (A). The SI unit for charge is the Coulomb (C). So the Ampere is 1 C per second.

Click image to view the movie - stupid.

There are insulators and Conductors, but there are also Not so good conductors. The impedance of the motion of Charge through a conductor Is the conductor’s resistance. Resistance is the ratio of the Potential difference across A conductor to the current It carries.

Ohm’s law states that the Resistance is constant over a Wide range of applied Potential differences. It is usually shown by… V = IR SI unit for resistance is the Ohm, And is represented by Ω.

Resistance depends on length, Cross-sectional area, material, And temperature. Resistors can be used to control The amount of current In a conductor.

The plate on an iron states that The current in the iron is 6.4 A PROBLEM... The plate on an iron states that The current in the iron is 6.4 A When the iron is connected across A potential difference of 120V. What is the resistance of the iron? R = 19 Ω

Electric power is the rate of Conversion of electrical energy. P = IV The SI unit is the Watt.

An electric space heater is Connected to a 120 V outlet. The PROBLEM... An electric space heater is Connected to a 120 V outlet. The Heater dissipates 3.5 kW of power In the form of heat. Calculate The resistance of the heater. R = 4.1 Ω

An electric circuit is a Continuous path through which Electric charges can flow. There are two types of circuit Connections… Parallel & Series

A parallel circuit is one with Several current paths, whose Total current equals the sum of the Currents in its branches.

A series circuit is one in which Current passes through one Device and then another.

Electric companies measure Energy consumption in Kilowatt-hours. 1 kW h = 3.6 X 106 J

Current moving through a resistor Causes it to heat up because Flowing electrons bump into the Atoms in the resistor. These collisions increase the Atoms’ kinetic energy and, thus, The temperature of the resistor.

P = I2R V2 R P = V2 R E = t If we rearrange Ohm’s Law, and The formula for power, we have 3 new formulas that we can use… And for the thermal Energy dissipated… P = I2R V2 R P = V2 R E = t

Power Electrical Energy is usually converted to Electromagnetic Energy (light), Thermal Energy (heat), or Kinetic Energy (motion).

A heater has a resistance of 10 Ω. It operates on 120 V. PROBLEM... A heater has a resistance of 10 Ω. It operates on 120 V. What is the power dissipated by The heater? What is the thermal Energy supplied by the heater In 10 s? 1.44 kW 14.4 kJ

Circuit = the path that flowing electrons follow If path is continuous, it’s a closed circuit and electricity can flow. If path is interrupted, it’s an open circuit and electricity can NOT flow.

Series Circuits Current goes through one pathway only. Same amount of current goes through each component (battery, resistor, etc.). The total resistance of resistors in series = the sum of each resistance (add them up).

In a series circuit, all of the Resistors are added together In order to get the Equivalent Resistance. R = R1 + R2 + R3 + … See that the equivalent resistance Is greater than any individual Resistor, therefore if the voltage Does not change, adding more Resistors always decreases current

Three 20 Ω resistors are connected In series across a 120 V generator. PROBLEM... Three 20 Ω resistors are connected In series across a 120 V generator. What is the equivalent resistance Of the circuit? What is the current In the circuit? R = 60 Ω I = 2.0 A

Parallel Circuits Current divides into 2 or more paths Voltage drop across components is equal. The sum of the current in each parallel path = the total current in (or out) of the circuit.

In a parallel circuit the resistance Is always smaller than any One resistor because there are More branches for the current To flow through. Equivalent Resistance for Parallel 1/R = 1/R1 + 1/R2 + 1/R3 + …

Three 15 Ω resistors are connected In parallel and placed across PROBLEM... Three 15 Ω resistors are connected In parallel and placed across A 30 V battery. What is the Equivalent resistance? What is the Current through the entire circuit? What is the current through each Branch of the circuit? R = 5 Ω I = 6 A I = 2 A

Draw a circuit diagram of a series circuit and a PROBLEM... Draw a circuit diagram of a series circuit and a Parallel circuit that each contain The following… Battery, motor, 3 lights, and 2 Resistors.

There are many safety devices When dealing with electrical Circuits. A short circuit is when the Resistance is very small which Makes the current very large.

When a short happens enough Thermal energy is produced to Start a fire, or just melt the Wires if you’re lucky. A fuse is used to help stop a short Before it gets too bad. When a fuse is connected to the circuit it will melt and “blow” Before the wires do.

A circuit breaker is another kind Of fuse. It breaks the circuit when the Current gets too high and a Switch flips. In order to fix The circuit, all you have to do is Flip the switch back.

An ammeter is a device used to Measure the current in a circuit. It is added in series and Has a low resistance. A voltmeter measures the Voltage of a circuit. It is added in parallel and has A high resistance (10 kΩ). A multimeter measures both And more.

Click image to view movie. Electric Motor Click image to view movie.

The wire coil in an electric motor is called the armature The wire coil in an electric motor is called the armature. The armature is made of many loops mounted on a shaft or axle. The magnetic field is produced either by permanent magnets or by an electromagnet, called a field coil. The torque on the armature, and, as a result, the speed of the motor, is controlled by varying the current through the motor.

Electromagnetic Induction After nearly ten years of unsuccessful experiments, Faraday found that he could induce electric current by moving a wire through a magnetic field. Electromagnetic Induction Click image to view the movie - stupid.

The difference in potential is called the induced EMF. When you move a wire through a magnetic field, you exert a force on the charges and they move in the direction of the force. Work is done on the charges. Their electrical potential energy, and thus their potential, is increased. The difference in potential is called the induced EMF.

Electric Generators The electric generator, invented by Michael Faraday, converts mechanical energy to electrical energy. An electric generator consists of a number of wire loops placed in a strong magnetic field. The wire is wound around an iron core to increase the strength of the magnetic field. The iron and the wires are called the armature, which is similar to that of an electric motor.

The armature is mounted so that it can rotate freely in the magnetic field. As the armature turns, the wire loops cut through the magnetic field lines and induce an EMF. Commonly called the voltage, the EMF developed by the generator depends on the length of the wire rotating in the field. Increasing the number of loops in the armature increases the wire length, thereby increasing the induced EMF.

Generators and motors are almost identical in construction, but they convert energy in opposite directions. A generator converts mechanical energy to electrical energy, while a motor converts electrical energy to mechanical energy

Electrons can move more freely in semiconductors than in insulators, but not as easily as in conductors. Atoms of the most common semiconductors, silicon (Si), and germanium (Ge), each have four valence electrons.

The conductivity of intrinsic semiconductors must be increased greatly to make practical devices. Dopants increase conductivity by making extra electrons or holes available

If an electron donor with five valence electrons, such as arsenic (As), is used as a dopant for silicon, the product is called an n-type semiconductor. If an electron acceptor with three valence electrons, such as gallium (Ga), is used as a dopant for silicon, the product is called a p-type semiconductor

Click image to view movie. Diodes Click image to view movie.

These diodes are called light-emitting diodes, or LEDs When electrons reach the holes in the junction, they recombine and release the excess energy at the wavelengths of light These diodes are called light-emitting diodes, or LEDs

Transistors and Integrated Circuits Click image to view movie.

Questions?

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