Review Warm Up

1. An object is dropped from rest from a height of 12 meters above the ground. The object falls freely and reaches the ground 1.1 seconds later. What is the average speed of the object?

2. According to the diagram below, what is the acceleration of the object?

5 N 18 N3. What is force of an apple at rest on a table?

15 kg

Semiconductors&

Transistors

A little more circuit Information

Semiconductors materials with an energy barrier such that only electrons with energy above a certain amount can “flow.”

**USED TO AMPLIFY AND CONTROL WEAK SIGNALS– Typically made of a poor conductor, such as

silicon, that has had impurities added to it. The process of adding impurities is called doping.

– As the temperature rises, more electrons are free to move through these materials.

Transistors are used to control large current output with a small bias voltage. – combination of differently “doped” materials

arranged in a special way– A common role of transistors in electric circuits is

that of amplifiers. – In that role, transistors have almost entirely

replaced vacuum tubes that were widely used in early radios, television sets, and computers.

Ch. 36

Magnetism

Magnetic Poles

• Regions around magnets that produce a magnetic force

Magnetic Fields• The space around a magnet in which force is

exerted• Magnetic field strength is measured using the unit

Tesla (T)

Magnetic Domains• Clusters of aligned atoms– Iron and other materials that can be magnetized

have domains in which the combined motion of electrons produces the equivalent of small magnets in the metal.

• When many of these domains are aligned, the entire metal object becomes a strong magnet.

• Magnetic effects result from the motion of electrical charges.

Electric Currents and Magnetic Fields

• Moving charges produce a magnetic fields

ElectromagnetCurrent carrying coil of wire with many loops

• The direction of the magnetic force is always perpendicular to the line of motion of the electric charges.

Magnetic Forces on moving charged particles

• Force is greatest at angles 90 to the field• Force is zero when the charged particle moves

parallel to the field

Magnetic Forces on Current Carrying Wire

Ch. 37 Electromagnetic Induction

Relative motion of a coil with respect to a magnet will induce voltage.

Faraday’s Law

The Induced voltage in a coil is proportional to the product of the number of loops and the rate at which the magnetic field changes within those loops

Generators

• Rotating a coil in a stationary magnetic field

Electromagnetic Waves

• A combined electric and magnetic field that travels through space

Electromagnetic Wave Propagation

• Can travel through matter & a vacuum• Can travel through nonconducting materials

known as dielectrics. – Example Air, glass, and water

Practice Problems

The End!!