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Questions and Answers
What component in a simple electrical circuit is used to control the amount of current?
What is the unit of electric current?
Through which component should an ammeter be connected in a circuit?
What is the conventional direction of current flow in a circuit?
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How is 1 milli-ampere written in terms of amperes?
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Which formula represents the electromotive force (EMF) in a system?
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What is measured in volts using a voltmeter in a circuit?
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How is the voltage available at the terminal of the source of supply denoted?
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What is electric current?
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What is a molecule?
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What is the charge of a proton?
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Which sub-atomic particle is electrically neutral?
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In an atom, where are the electrons located?
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What is the K shell?
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Which of the following is a common conductor?
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Which of these materials is an insulator?
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Which element is a common semiconductor?
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How many electrons does the 'L' shell in a copper atom hold?
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Study Notes
Structure of Matter
- Matter is anything that has mass and occupies space.
- A matter is made of tiny, invisible particles called molecules.
- A molecule is the smallest particle of a substance that has the properties of the substance.
- Each molecule can be divided into simpler parts by chemical means.
- The simplest parts of a molecule are called atoms.
Atomic Structure
- An atom contains three types of sub-atomic particles: electrons, protons, and neutrons.
- Protons and neutrons are located in the centre or nucleus of the atom.
- Electrons travel around the nucleus in orbits.
- Nucleus contains protons and neutrons in equal numbers.
- Protons have a positive electrical charge and are almost 1840 times heavier than electrons.
- Electrons have a negative electric charge and are three times larger in diameter than protons.
- Neutrons are electrically neutral.
Energy Shells
- Electrons are arranged in shells around the nucleus.
- A shell is an orbiting layer or energy level of one or more electrons.
- Major shell layers are identified by numbers or by letters starting with 'K' nearest the nucleus and continuing alphabetically outwards.
- There is a maximum number of electrons that can be contained in each shell.
- Example: a copper atom with 29 electrons would have four shells with a number of electrons in each shell.
Conductors
- Conductors are materials that have many valance electrons, permitting electrons to move through them easily.
- Generally, conductors have one, two, or three electrons in their shells.
- Most metals are conductors.
- Examples of good conductors: Copper, Aluminium, Zinc, Lead, Tin, Eureka, Nichrome, etc.
- Silver and gold are very good conductors.
Insulators
- Insulators are materials that have few, if any, free electrons and resist the flow of electrons.
- Generally, insulators have five, six, or seven electrons in their shells.
- Examples of insulators: air, glass, rubber, plastic, paper, porcelain, PVC, fibre, mica, etc.
Semiconductors
- Semiconductors are materials that have some of the characteristics of both conductors and insulators.
- Semiconductors have valence shells containing four electrons.
- Examples of pure semiconductor materials: silicon and germanium.
Simple Electrical Circuit
- A simple electrical circuit consists of:
- An energy source (cell) to provide voltage needed to force the current through the circuit.
- Conductors through which the current can flow.
- A load (resistor 'R') to control the amount of current and to convert electrical energy to other forms.
- A control device (switch 'S') to start or stop the flow of current.
Electric Current
- Electric current is the flow of free electrons in a definite direction.
- Current is defined as the amount of charge 'Q' transferred over a time 't'.
- Conventional flow of current is opposite to the direction of the flow of electrons.
- Unit of current (I) is an ampere (A).
- Multiples of the ampere: 1 kA = 1000 A, 1 mA = 1/1000 A, 1 μA = 1/1000000 A.
Electromotive Force (EMF)
- EMF is the electrical force that causes free electrons to move in a conductor.
- Unit of EMF is 'Volt' and is denoted by letter 'E'.
- EMF cannot be measured by any meter, only calculated using the formula E = V + IR.
Potential Difference (PD)
- Potential Difference is the difference of voltage and pressure across two points in a circuit.
- Measured in volts.
- Calculated using the formula EMF = V1 + IR.
Terminal Voltage (p.d)
- Terminal voltage is the voltage available at the terminal of the source of supply.
- Symbol is VT and unit is also the volt.
- Calculated using the formula V1 = EMF - IR.
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Description
Learn about the basics of electricity, including electric current, static electricity, and the structure of matter, including molecules and atoms.
