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Introduction

Activity

Think of any places where we have safety rules.

LESSON OBJECTIVES

By the end of this topic you should be able to:

• Set up simple electric circuits
• Identify circuit symbols
• Define electric current

Electric Current

Electric current is defined as the rate of flow of charge.
I is used as a symbol for current

Current is measured in amperes. Symbol for amperes is A.
Current = Charge flowing/time taken
I =   a/t  or  a = It
The S.I. unit of charge is and time is seconds.

You are provided with the following

Bulb- A, Bulb - C and Cell

Prior Knowledge

What is science?

Objectives

By the end of this lesson you should be able to:

1. Explain what the study of physics involves.
2. Relate physics to other subjects and technology.
3. Identify career opportunities in physics.

Activity 1

Drag a conducting wire so that it connects the positively charged body and the negatively charged body

An electric current is produced when charges move in a definite direction.
A complete path along which the charges flow is called an electric circuit
.

Connecting a Circuit

In connecting a circuit, it is advisable to arrange the components according to the circuit diagram given. Then connect a wire at one point and proceed in one direction till the loop is completed. This procedure is illustrated in the animation below.

The function of a cell is to maintain a continuous flow of charge round the circuit by providing electrical energy.

Simple Electric Circuit

Observe the dry cell, the switch and the bulb. What happens to the bulb?

Observation

Once the circuit is complete, with items or components in place, the bulb lights.

Conclusion

Current does not flow in an incomplete circuit.

Activity 4

Click the switch in the circuit below so that the circuit is complete.  Observe what happens tothe bulb?

Electrons flow from the negative terminal of the cell to the positive terminal through the connecting wire.
By convection the current is considered to flow to flow from positive terminal to the negative terminal through the connecting wires.

Activity 4

Observe what happens to the bulb.

Electrons flow from the negative terminal of the cell to the positive terminal through the connecting wire. By convention, the current is considered to flow from positive terminal to the negative terminal through the connecting wires.

Circuit symbols

Circuit symbols are used instead of real pictures of the components

Components and their symbols

Parallel and Series Circuits

Activity 3

In the following animation the moving arrow represents the flow of electric current in parallel and series circuits. What do you notice as the main difference between parallel and series circuits? Identify one difference in the flow of current between the parallel and series circuits.

Discussion

In a parallel circuit, a wire carrying an electric current is branched into two or more paths. That is, there are current junctions in the circuit. This is comparable to road junctions. In this case, current divides into smaller parts to travel through the branched paths. These parts recombine as they pass through the source, and the process continues. In series circuit, the same current flows through all the points in a circuit without dividing.

Activity 4 : Arrangement of cells in parallel

Drag and drop a cell into gap A.

Observe the brightness of the bulb.

Drag and drop a cell into gap B, followed by gap C and each time observe the brightness of the bulb.  Positive ends of the cell should face the same direction.  They are said to be in parallel.

Activity 5 : Arrangement of bulbs in series

Click on the bulb, then drag and drop it in gap A.

Click on the wires then drag and drop them in gaps B and C so that the circuit is complete.  Observe the brightness of the bulb.

Drag the wire in gap B away; then drag and drop a bulb into the gap.
Observe the brightness of the two bulbs.

Drug away the wire in gap C and replace it with a bulb so that you have three bulbs in series. Observe the brightness of the bulbs.

Activity 6 : Arrangement of bulbs in parallel

Drag and drop a bulb in gap X.
Observe the brightness of the bulb.

Drag and drop a bulb in gap Y and Y respectively, each time observing the brightness of the bulb.

Fill the gaps in the table by dragging the words brighter or same brightness in the spaces

The brightness of the bulbs remain the same throughout.

Drag out the bulb in gap Y. What happens to the others?
Their brightness increases.

The brightness of a bulb is a measure of how much electric current is passing through it.

If bulbs are in parallel a fault in one bulb does not affect the others.

Electric Current

Electric current is defined as the rate of flow of charge. Its conventional symbol is I.

Current is measured in amperes, conventionally represented by A.

The amount of current can be calculated from

Current = Charge flowing/Time taken. That is,

I = Q/t (and Q= It)

The S.I. unit of charge is the coulomb, C.

Activity 7: Circuit symbols

Circuit symbols are used instead of real pictures of the components.

Some electrical Components and their symbols

Activity 8 : Arrangement of cells in series

Drag and drop a cell into gap X and the wire into gap Y so that the circuit is complete. Observe the brightness of the bulb.

Drag the wire out and replace it with another cell so that the positive of one cell is connected to the negative of the other cell. This arrangement is called series arrangement.

Physics as a science

In your primary school you learnt about living things and non-living things. The science that deals with living things is called biological science while that which deals with non-living things is called physical science. Physical science is further divided into chemistry and physics. While chemistry is the study of substances and how they react with each other, physics is the study of matter and how it relates to force and energy. The following figure represents the branches of science.

Branches of Physics

Physics can be illustrated as a tree with many branches.

Physics and Technology

Some areas of physics are used in technology. Technology is the application of science; and it includes road construction, communication, aviation and medical technology, among others. The ultrasound scanner, X-ray tube and stethoscope used in hospitals are examples of applications of physics in medical technology.

Stethoscope

Aviation

Physics and other Subjects

Knowledge of physics is also applied in other subjects. The principles of electrostatics and particulate nature, for example, are used to explain reactions in chemistry. The tools, implements and farm machinery learnt in agriculture as well as the process of dating historical remains are applications of physics.

Combine harvester

Careers in Physics

Physics is related to many careers in life, and these include engineering, Communication Technology, architecture, teaching, medicine, meteorology and astronomy, among others.

Communication

Medicine

Pedestrian crossing

Animal crossing

Railway crossing

Laboratory Rules

Rule 1: Proper dressing and closed shoes should be worn, long hair tied and shirts and blouses tucked in.

Explanation: Long hair or loose hair can get caught by turning parts of apparatus, catch fire, get into acid or pull the apparatus down

Rule 2: Handle electrical apparatus with dry hands. Do not splash water where electric sockets are located.

Explanation: Electric shock can kill. Water conducts electricity.

Rule 3: Hands must be washed before leaving the laboratory.

Explanation: The hands can be contaminated by chemicals.

Rule 4:There should be no eating or drinking in the laboratory.

Explanation: Chemicals in the laboratory can contaminate the food and lead to food poisoning.

Rule 5:Know the location and working of switches, fire fighting equipment, First Aid kit, gas supply and water supply points.
Explanation: For quick action during any fire outbreak.

Rule 6 Keep the floors and working surfaces dry. Any spillage should be wiped off immediately.

Explanation: Wet surfaces are slippery and can cause accident.

Rule 7Any instruction given must be followed carefully. Never attempt anything when in doubt.

Explanation: Can get wrong results or cause harm to oneself and others.

Rule 8: Practical jokes are not allowed in the laboratory.

Explanation: Such jokes can be dangerous.

Rule 9 Never play or run in the laboratory

Explanation: To avoid falling or knocking down the apparatus or equipment, most of which are delicate.

.

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