Tribal Challenge Review Question!

A satellite is in circular orbit 525km above the surface of the Earth. Determine the satellite’s (a) speed and (b) period of revolution.

(3 points – first Tribe with a correct answer)

(1 point – every Tribe with a correct answer after that)

Tribal Challenge Review Question!

A satellite is in circular orbit 525km above the surface of the Earth. Determine the satellite’s (a) speed and (b) period of revolution.

Solution: (a) 7.6 x 103 m/s

(b) 5.71 x 103 seconds (or 1.59 hours)

Electricity Review and Coulomb’s Law

SPH4U – Grade 12 Physics

Unit 1

Electrostatics

Electrostatics -- The study of electric charges that are stationary. (not moving)

Electric Charge -- is a property of matter that is responsible for all electric and magnetic forces and interactions.

Electrostatics

Electric charge is described as negative or positive.

Static Electricity -- A buildup of stationary electric charge on a substance.

Electrical Structure of Matter

The Bohr-Rutherford model of the atom can help us understand electrical phenomena. The principal concepts to know are: Matter is composed of sub-microscopic particles

called atoms. Electric charges are carried by particles within the

atom that are called electrons and protons. Protons are found in a small central region of the

atom called the nucleus. They are small, heavy particles, and each one carries a positive electric charge of a specific magnitude, called the elementary charge.

Electrical Structure of Matter

Electrons move in the space around the nucleus. They are small, very light particles (each with only slightly more than 1/2000 the mass of a proton), yet each of them carries a negative electric charge equal in magnitude to that of the proton.

Atoms are normally electrically neutral, because the number of (positive) protons in the nucleus is equal to the number of (negative) electrons in the space around the nucleus.

Neutrons are small, heavy particles (each slightly heavier than a proton) found in the nucleus. The carry no electric charge.

Electrical Structure of Matter

If an atom gains an extra electron, it is no longer neutral but has an excess of electrons and a net negative charge. Such an atom is called a negative ion.

If an atom loses an electron, it will have a deficit of electrons and a net positive charge. Such an atom is called a positive ion.

Law of Electric Charge

The law of electric charge states that opposite electric charges will attract each other, and similar electric charges will repel each other.

Opposite electric charges Attract + -

Similar electric charges Repel + +

Charged objects (positive or neg.)

Attract Neutral Objects

+ Neutral

Law of Conservation of Charge

The Law of Conservation of Charge states that charge can transferred from one object to another but the total charge of a closed system remains constant.

How to Charge an Object

Recall: There are three main ways to charge an object:FrictionContact Induction

The Coulomb

The unit we use to measure electric charge is called the Coulomb (C).

(e) is the charge on a single electron. All other electric charges are simple multiples of this smallest charge.

e = 1.60 x 10-19 Coulombs 1 Coulomb = 6.24 x 1018 e.

The Coulomb

If Q is the amount of charge on an object (measured in Coulombs), and N is the number of elementary charges, then Q = Ne.

** When there are extra electrons, e and Q are negative.

When there are electrons missing, e and Q are positive.

Electric Current An electric current is defined as the number of

electrons moving in the same direction past a certain point in one second. The symbol for electric current is I. Electric Current is measured in Amps. (A).

The electric current I through the wire is measured as the total charge Q (in coulombs) moving through an area of wire in a time Δt (in seconds).

t

QI

Coulomb’s Law

Coulomb’s law: the force between two point charges is inversely proportional to the square of the distance between the charges and directly proportional to the product of the charges.

Coulomb’s law only applies to point charges, or to situations where particles are much, much smaller than their distance of separation.

221

r

qqkFE

Note that k = 8.99 x 109 N-m2/kg2

The Superposition Principle

In nature, rarely will you ever be dealing with the interaction of just two particles. Often more than two particles are interacting.

How do you calculate the force on a particle when there are more than two particles present?

Answer: We use the superposition principle. We find the sum of all the forces acting on the particle.

The Superposition Principal

Ex.1 Three particles (all with the same mass) q1, q2, and q3 are located as shown in the diagram below in a straight line. What is the total force being felt by q2?

1.0 m

q1 q3q2

2.0m

q1 = 2 x 10-6 C

q2 = -1 x 10-6 C

q3 = -1 x 10-6 C

Electrostatic Equilibrium

Ex.2 Three particles, q1, -2q, and q3 are located as shown in the diagram below (q is positive). They are all in an exact line. If the total electric force on q3 is zero, determine where q3 must be located.

1.0 m

q3 -2qq1

?

In Two Dimensions

Ex. 3 Three spheres, each with a negative charge of 4.0x10-6C, are fixed at the vertices of an equilateral triangle whose sides are 0.2m long. Calculate the magnitude and direction of the net electric force on each sphere.

Homework

Read Sections 7.1, 7.2. Make additional notes to supplement the lesson notes.

Complete the following questions:Pg. 326 # 2, 9Pg. 333 # 2, 3, 7, 9