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Class VI - Science: Simple Electric Circuits
One Word Answer Questions:
Q) Which part of an electric bulb is connected to the terminals?
    
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Q) Name the device which is used to break the electric circuit or to complete it?
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Q) Name the device which allows the passage of electricity.
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Q) Give an example of an insulator?
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Q) Can electric current pass through a sheet of rubber?
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Short Answer Questions:
Q) Define Conductors and Insulators?
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Q) What is a Filament?
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Q) State one activity to prove that air is an insulator.
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Q) What is a fused bulb? What happens to the electric cell when a bulb is fused?
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Q) Explain briefly why the handles of tools like screw drivers and pliers used by electricians are covered with plastic?
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Q) What is the purpose of using an electric switch? Name some electrical gadgets that have switches built into them?
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Q) Would the bulb glow in the circuit in which wool is used to connect the battery and bulb?
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Q) In which ways the cells are joined in a torch?
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Long Answer Questions:
Q) Why are conductors and insulators equally important? Give reasons?
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Q) Explain briefly the working of a torch bulb?
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Story of bulb
  • Thomas Alva Edison who ultimately succeeded in making the first bulb.
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  • From childhood, Edison was of an inquisitive nature and he learned science by performing experiments himself.
  • Even an intelligent scientist like Edison had to work hard for many years before he could make a bulb that worked.
  • First of all, he passed electricity through a thin, threadlike platinum wire.
  • ts_sec2.jpg

  • He noticed that the wire did give out light after being heated, but it burned out after only a few seconds.
  • Edison then thought that if the air surrounding the wire coil was removed then, perhaps, the wire would not burn out so quickly.
  • He made a glass casing and fitted a filament of platinum wire in it.
  • He then removed all the air from within the glass casing.
  • He passed an electric current through the wire and, to his delight, the bulb lit up and did not burn out for eight long minutes.
  • He began experimenting with different materials while searching for a better choice of filament.
  • He tried cotton thread coated with soot.
  • This filament burned continuously for 45 hours.
  • He tried different kinds of thread. One summer day he saw a man fanning himself with a bamboo fan.
  • An idea stroked his curious mind - "Well, why not try bamboo fibre as a filament?" He executed his idea and amazingly the bamboo filament burned continuously for a number of days.
  • Finally he succeeded in making a cotton filament that was even better than the bamboo one.
Introduction

Electricity is very essential to us for many purposes. Electric bulbs, fans, televisions, refrigerators, air conditioners, mixers and juices all work on electricity.Electricity is generated in power stations and brought to our houses by wires.

Electric Cell And Torch Bulb
Electric Cell
  • An electric cell is a device that supplies electrical energy to devices that function using electricity.
  • It provides electricity to a number of devices, such as toys, alarm clocks, pocket radios and cameras.
  • An electric cell consists of two terminals: a positive terminal and a negative terminal.
  • It has a cap, just under which there is a plus sign. This is the positive terminal of the cell.
  • At the other end of the cell, there is a flat metallic disc with a minus sign just above it.
  • This metallic disc is the negative terminal of the cell. These terminals of the cell can be used to connect it to various devices.
  • Inside a cell, there is dark powdery stuff, which is the chemical that helps the cell to provide electricity to the device it is connected to.
  • When a cell is connected to a device, the strength of the chemical decreases.
  • Finally, when the entire energy of the chemical is spent, the device connected to the cell stops functioning.
  • A rechargeable cell or a storage battery can be recharged and can be used again.
battery
An Electric Cell

A Bulb Connected To An Electric Cell
Torch Bulb:
Inside view of a torch:
torch

  • A torch bulb consists of two terminals and a filament.
  • The filament is a spirally wound wire inside the bulb supported by two thick wires at its ends.
  • When the positive and the negative terminals of an electric cell are connected to the two terminals of a bulb, electricity passes through the filament and it starts glowing.
  • The terminals of the bulb are fixed in such a way that they do not touch each other.
  • In recent years, a different type of bulb has become popular - the compact fluorescent lamp (CFL).
  • It is an energy-saving bulb, which has a longer life than an ordinary bulb.
  • bilb
    A Torch Bulb Connected To An Electric Cell
    filament
    A torch Bulb(a) And(b) Its Inside View
    cfl
    CFL To An Electric Cell
Activity
  • Simple electric circuits Take four wires of different colours, say blue, green, red and yellow, each about 15 cm long.
  • Electric wires are often covered with plastic.
  • First, remove about two centimeters of the plastic covering from both ends of each wire.
  • Now attach two wires (Blue and Green) to a bulb and two wires (Red and Yellow) to a cell with a cello tape or cell holder as shown in .
  • We can use a cell holder to hold the cells and wires together tightly.
  • Take an old inner tube of a bicycle and cut it into narrow bands.
  • Each band should be wide enough to cover the knob of the cell.
  • This is your cell holder. Now connect the wires in different forms.
  • In each case, check whether the bulb glows or not.
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  • In which case does the bulb glow? Why? In which case the bulb does not glow? why?
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  • You may observe that the bulb glows in connections shown in (d) and (e), but not in other cases? We observe that in (d) and (e) the connections form a closed path while in the remaining cases we find some gap in the path.
What is a circuit?
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  • A simple electric circuit.
  • It consists of a cell (power source), a bulb, and connecting wires.
  • An electric circuit provides a complete path for electricity to flow between cell and the bulb.
  • A similar circuit exists for an electric bulb which we use in our houses.
  • The two electric supply wires (called live and neutral) are connected to the two terminals of the bulb through a switch.
  • When the switch is closed (put on) the circuit provides complete path for electricity.
Electric Circuit

  • Electricity needs a path to flow from the positive terminal to the negative terminal of an electric cell.
  • "A connection that provides a path outside an electric cell, for the electricity to flow from the positive terminal to the negative terminal of the cell, is called an electrical circuit".
  • For example, a bulb glows only when the positive terminal and the negative terminal of an electric cell are connected to the two terminals of the bulb.
  • If the wires from the bulb are connected to the same terminal (either positive or negative), then the bulb does not glow.
  • Sometimes, the bulb may not glow even though the connections are properly made.
  • This may be because the flow of electricity is incomplete as the filament in the bulb is broken. A bulb with broken filament is said to be fused.
circuit
Closed And Open Circuit
directioncurrent
Direction Of Current In An Electric Circuit
Electric Switch

"A device that is used to stop the flow of electricity by breaking the circuit is called a switch".
Switches have wide range of applications. Some common types of switches are:

  • Toggle switches, which are used in our houses.
  • Push button switches, which are used in the starter of a water pump.
  • Joystick switches, which are used in the remote control unit of a toy car.
Making a switch:

We need the following to construct an electric switch:

  • Thermocol Piece,
  • A pair of thumb tacks,
  • A metal paper clip,
  • Four pieces of insulated wire,
  • An electric cell and
  • A torch bulb.
    ‣ We start by creating the circuit. There will be one difference, though. We will leave one of the wires of the electric cell and the bulb unconnected.
    ‣ We connect one end of the loose wire from the cell to a thumb tack, which is fixed on the thermocol.
    ‣ Now we connect one end of the loose wire from the bulb to another thumb tack fixed to the thermocol close to the thumb tack fixed earlier.
    ‣ The distance between the two thumb tacks should be less than the length of the paper clip. The switch is ready.
    ‣ When we want to switch the bulb on, just bring the paper clip in contact with the thumb tack.
    ‣ This completes the circuit and the bulb starts glowing. To click it off, take the clip away from the thumb tack.
switch

An Electric Circuit With A Switch
Electric Conductors And Insulators:

"Materials that allow electricity to pass through them are called conductors".

  • Since metals are good conductors of electricity, electrical wires are made up of metals.
  • These conducting wires are used to connect various components of an electrical circuit.
  • Copper, silver, gold and aluminium are a few examples of electrical conductors.
  • Copper is the most commonly used material for making connecting wires.
  • Sometimes we get electric shocks because our bodies are also good conductors of electricity.

"Materials that do not allow electricity to pass through them are called insulators".

  • Some common insulators are glass, air, plastic, cotton, thermocol, wood and rubber.
  • As insulators do not conduct electricity they are used to protect us from the dangerous effects of electricity.
  • Without the help of insulators, the use of electrical appliances is impossible.
  • Tap water is a good conductor of electricity, but distilled water (water in it its purest form), acts as an insulator. Distilled water is, therefore, used in batteries as an insulator.
  • We use various electrical appliances every day. The parts of the electric appliances that we touch are covered with insulating material.
  • For example, plugs and switches are covered with an insulating material such as plastic, and the wire attached to the plug has a metal wire inside it, which is a conductor. So conductors and insulators work hand in hand.
switch

Conducting Substances Are Always Coated With Non-Conducting Materials
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