SCIENCE CH-12 ELECTRICITY AND CIRCUITS (NOTEBOOK AND WORKBOOK EXERCISE)
CH-12 ELECTRICITY AND CIRCUITS (NOREBOOK AND WORKBOOK EXERCISE)
NOTE: IT IS COMPULSORY TO DRAW DIAGRAMS GIVEN ( CAN COLOUR THEM TOO)
NEW WORDS
insulators
filament
socket
inventors
conductors
NEW TERMS
Inventor: a person who invented a particular device
Terminal: starting or ending point
Answer the following questions in one word or one sentence.
a. What forms the negative terminal of a dry cell?
ANS. The outer covering of a dry cell consists of a zinc metal which acts as the negative terminal for the cell and this is indicated by a negative sign (-).
b. Give one example of a conductor.
ANS. All metals, impure water, graphite are examples of conductor.
c. What are insulators?
ANS. The materials that do not allow an electric current to pass through them are called insulators. Wood, cotton, plastic, rubber, distilled water and glass are some insulators.
d. In which direction does a current flow in a circuit?
ANS. The current flows from the positive terminal of the cell to its negative terminal.
e. What is the central part of an atom made up of protons and neutrons called?
ANS. Protons and neutrons form the central part of the atom called the nucleus.
Answer the following questions in short.
a. What is an electric circuit? State its components.
- ANS. A bulb glows when a path is provided for the electric current to flow from the positive terminal to the negative terminal of a cell. The complete path through which an electric current flows is called an electric circuit.
- An electric circuit consists of the following components: • A source of electric current (i.e., electric cell or battery) • Connecting wires • Electric bulb • Switch
- DRAW THE DIAGRAM GIVEN BELOW
b. State the differences between conductors and insulators.
ANS. The materials that allow an electric current to pass through them are called conductors.
ex. All metals, salt solutions, impure water are good conductors of electricity.
The materials that do not allow an electric current to pass through them are called insulators.
ex. Wood, cotton, plastic, rubber, distilled water and glass are some insulators.(bad conductors)
c. State the differences between an open circuit and a closed circuit.
ANS. In an open electric circuit [Fig:(a).] the electrical point of contact is broken as the switch is open (turned off) so the current does not flow.
In a closed electric circuit [Fig: (b)] as the switch is closed (turned on), current flows from the positive terminal of the cell to its negative terminal.
DRAW THE DIAGRAM BELOW
d. Name the two types of electric cells. State one difference between them.
ANS. . The electric cell which we use in alarm clocks, torches etc. is also called a dry cell. A dry cell cannot be recharged and is also known as a primary cell.
The type of electric cell that can be recharged is called a secondary cell. Secondary cells are also known as lead-acid accumulators. Car batteries are examples of secondary cells.
e. What is an electric current? List some sources of electric current.
ANS. An electric current is the flow of charge due to electrical energy.
Sources such as oil, gas, coal, and wood. Natural resources such as the Sun, wind, water and nuclear energy are also used to generate electricity.
The electricity that comes to our homes is generated at the power house stations.
Cells and batteries are the most commonly used sources of electric current. For small household devices like radio, toys, torches, wrist watch, alarm clock, etc., an electric cell or a battery (no. of cells) is used.
Give reasons.
a. Wires have a plastic or rubber covering.
ANS. Electric wires are made of metals such as copper and are coated with rubber or plastic to protect us from getting electric shocks as the plastic is insulator and it does not allow electricity to pass through it.
b. Copper wire is used instead of wood in an electric circuit.
ANS. Copper wire is used instead of wood in an electric circuit because copper is good conductor of electricity and it will allow the current to pass through it whereas wood is an insulator which does not allow the current to pass through it.
c. It is advisable not to put our hands inside a plug socket.
ANS. Do not put your finger inside a plug socket especially when it is ON as there is flow of current inside it and we can get an electric shock.
d. Tungsten is used as a filament in a bulb.
ANS. The filament is made up of a metal called tungsten. Tungsten has a high melting point, and hence it does not melt even when the filament glows at a very high temperature.
Answer the following questions in detail.
a. List out the safety measures that should be followed while handling electrical appliances.
- ANS. Never touch or repair any electrical switches or plugs with wet hands.
• Do not put your finger inside a plug socket especially when it is ON.
• Always use rubber gloves or wear rubber footwear while handling electrical circuits.
• Disconnect the power source whenever repairing or handling any electrical device.
• Do not stick a metal object into any electrical appliance.
- Do not take out the wire when the switch is on.
• If you notice a spark in a switch, put it off immediately with the help of a wooden stick.
• In case of a fire in electric wires, never use water to extinguish it, as water is a good conductor of electricity. Instead use dry sand to extinguish the fire.
b. Explain the working of a bulb.
ANS. Electricity passes through the filament of the electric bulb as a result of which, it gets heated up and gives out light.
The filament is made up of a metal called tungsten. Tungsten has a high melting point, and hence it does not melt even when the filament glows at a very high temperature.
The filament is fixed to two thicker wires making a ‘V’ shape.
One wire touches the bottom of the bulb and the other touches the metal casing.
The bottom of the bulb and the metal casing act as the positive and negative terminals of the cell of the bulb.
These two terminals are fixed in such a manner that they do not touch each other. When the two terminals are connected to a source of current, the electricity starts flowing and the bulb glows.
DRAW THE DIAGRAM GIVEN BELOW.
c. Explain the structure of a primary cell.
ANS. Structure of a dry cell (PRIMARY CELL)
The outer covering of a dry cell consists of a zinc metal which acts as the negative terminal for the cell and this is indicated by a negative sign (-).
At the centre of the container a carbon rod is placed which acts as the positive terminal.
A metal cap with a positive (+) sign connected to the carbon rod indicates the positive terminal of the cell. Inside the container there is a dry or semi-solid paste of different chemicals.
These chemicals react with each other and an electric current Is produced.
DRAW THE DIAGRAM GIVEN BELOW
Diagram based questions.
a. Identify the picture/s in which the bulb will glow. Give reasons for your answer.
WORKBOOK EXERCISE LINK