Lesson Notes By Weeks and Term - Senior Secondary School 1

SUBJECT: PHYSICS

CLASS:  SS 1

DATE:

TERM: 2nd TERM

REFERENCE BOOK

• New School Physics By M.W Anyakoha
• Senior Secondary School Physics By P.N Okeke

 
WEEK 8

TOPIC: FIELD - CONCEPT AND TYPES OF FIELD. GRAVITATIONAL AND MAGNETIC FIELD. FORCE OF GRAVITY

CONTENT

• Concept of Field

• Types of Field

• Gravitational Field

• Concept of Field

Field can be defined as the region or space under the influence of some physical agency such as gravitational, electricity and magnetism.

• Types of Field

Fields are of various types namely: gravitational, magnetic and electric field.

• Gravitational Field

Gravitational field is any region or space around a mass in which the gravitational force of the mass is felt.

If we throw up massive objects, it is our common observation that they move up to their highest points, stay stationary very briefly and eventually move downwards, falling faster and faster until they hit the ground level. The up and down movements objects on the earth’s surface are subject to the influence of the gravitational field.

Force of Gravity

The force of gravity is the pull of attraction between the earth, itself and objects on or near it.

Newton’s Law of Universal Gravitation

Newton’s law of gravitation states that the force of attraction between two bodies of mass M1 and M2 is inversely proportional to the square of their distance R, between their centres and it is directly proportional to the product of their mass.

Mathematical expression

    F α  M1 M2R2                    F =  GM1 M2R2

Where F is the gravitational force on either particle, M1 and M2 are their masses, R is the distance between them, and G is a universal gravitational constant, whose numerical value depends on the units in which the force, mass, and length are expressed.

Acceleration Due to Gravity

The acceleration of objects due to the earth’s gravitational attraction is called the acceleration due to gravity. It is represented by the symbol g whose average value is about 9.81ms−2.

Without air resistance, different mass or objects released from rest at the same point will fall to the ground at the same time (free fall).

EVALUATION

1. Define field.
2. State Newton’s law of gravitation.

Magnetic Field

The region or space around a magnet in which the influence of the magnet can be felt or detected is called a magnetic field. If a white sheet of paper is placed over a magnet and iron fillings are sprinkled on the paper, it will be observed that the iron filings will arrange themselves in a definite pattern which illustrates the magnetic lines of force of the magnet. A similar pattern can be obtained by using the compass needle to plot the magnetic lines of force.

Fig 3.0 Magnetic Lines of Force Round a Bar Magnet

Lines of Force

A line of force is an imaginary line drawn in such a way that its direction at any point, that is the direction of the tangent, is the same as the direction of the field at that point.

EVALUATION

1. Define magnetic field.
2. Define gravitational field.

Reading Assignment

New School Physics pg 67 - 70

WEEKEND ASSIGNMENT (THEORY)

• Define A. gravitational field B. acceleration due to gravity. How does acceleration vary with latitude

• A. Explain what is meant by a field as used in physics. B. Mention three types of field known to you