Kerala Syllabus Class 7 Basic Science: Chapter 03 The World of Electricity - Questions and Answers

Questions and Answers for Class 7 Basic Science (English Medium) വൈദ്യുതിയുടെ ലോകം | Text Books Solution Basic Science (English Medium) Chapter 03 The World of Electricity - Teaching Manual | Teachers Handbook

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ഈ ബ്ലോഗ് ഉടമയുടെ രേഖാമൂലമുള്ള അനുമതിയില്ലാതെ ഈ ബ്ലോഗിൽ നൽകിയിരിക്കുന്ന ചോദ്യോത്തരങ്ങൾ, ഇതേരീതിയിലോ പി.ഡി.എഫ് രൂപത്തിലോ, മറ്റേതെങ്കിലും ഡിജിറ്റലോ, പ്രിന്റഡ് ഉൾപ്പെടെയുള്ള ഏതെങ്കിലും രൂപങ്ങളിലേക്കോ മാറ്റി മറ്റൊരു വെബ്സൈറ്റിലോ, ബ്ലോഗിലോ, യുട്യൂബ്, സോഷ്യൽ മീഡിയാ ഗ്രൂപ്പുകളിലോ ഉൾപ്പെടെ ഒരിടത്തും പ്രചരിപ്പിക്കാൻ പാടില്ലാത്തതാകുന്നു.

Std 7: Basic Science Chapter 03: The World of Electricity - Questions and Answers
♦ What do we usually do to get light when there is a power failure?
• Candles are used
• Emergency lamps are used 
• Kerosene Lamps are used

♦ What are the things needed to make an emergency lamp?
• Frame
• Rechargeable battery
• Switch
• Wires
• LED Module

♦ What are sources of electricity?
Devices that provide electricity are termed as sources of electricity. 
E.g.: Electric cells, generators, solar cells etc.

♦ What are electric cells?
• Electric cells are devices that can convert chemical energy into electrical energy. 
• Electrical energy is stored as chemical energy in them. This chemical energy is converted into electrical energy when we use them.

♦ What is the difference between cells and batteries?
A battery is an arrangement made by connecting more than one cell into a single unit. 
♦ Observe the pictures (A, B, C) in which the cells are connected in three different ways. 
• Do all of them represent the right way for making a battery? 
Answer: No

• Which among them is wrong? 
Answer: B

• Which one will give more electricity?
Answer: C
♦ Observe the pictures given below.
• From which source do these two devices get electricity?
Answer: Battery

• What is the difference between the sources of electricity used in these devices?
Answer: A cell in a clock cannot be used again when its charge is completely used up. But the battery in mobile phones can be recharged and used again.

♦ You may be using rechargeable and non-rechargeable cells in different devices at home. Classify them
Rechargeable Cells:
• Mobile phones
• Emergency lamps
• Laptops
• Power banks
• Hearing aids 
• Cameras 
• Smart Watches 

Non-Rechargeable Cells:
• Flashlights
• Toys 
• Alarm clocks
• Remote controls 
• Watches 

♦ What are the advantages of using LED? 
• L E D (Light Emitting Diode) helps to save energy considerably.
• LED bulbs require less energy than CFL. 

♦ What is LED module?
LED module is an arrangement of more than one LED bulb in a strip.  

♦ What is Electric Circuit?
Electric circuit is an arrangement that passes electricity from an electric source to a device. A circuit requires at least an electric source, connecting wire and an electric device
♦ Observe the following pictures. Parts of certain circuits are represented in the pictures given below.
♦ Will the bulbs in these circuits glow? Why? 
No, If the circuit is not complete, it is an open circuit. Electric devices can work only in a closed circuit.

♦ What is meant by Closed Circuit and Open Circuit?
A circuit is a closed one if it is complete. If the circuit is not complete, it is an open circuit. Electric devices can work only in a closed circuit.

♦ Are the following circuits closed or open? Why?
• Circuit one - open circuit
• Circuit two - closed circuit
The bulb lights up because the second circuit is closed.

♦ What is switch?
Switch is a device used to make a circuit closed or open when required. A circuit becomes closed when switch is turned on. It becomes open when switch is turned off.

♦ Take the 9 V battery, connecting wire and the LED module from your Science Kit. Arrange them as shown in the figure.
Connect the ends marked  A and B using different materials.
Materials: Safety pin, a piece of wood, paper, steel scale, charcoal, pencil graphite, plastic bangle, metal bangle, wet paper, copper wire. Tabulate your observations.
Material used Observation Inference
PaperThe LED module did not glowdoes not conduct electricity
Safety pinThe LED module glowconduct electricity
A piece of woodThe LED module did not glow does not conduct electricity
Steel scaleThe LED module glowconduct electricity
CharcoalThe LED module glowconduct electricity
Pencil graphiteThe LED module glowconduct electricity 
plastic bangleThe LED module did not glowdoes not conduct electricity
metal bangleThe LED module glow conduct electricity 
wet paperThe LED module glow conduct electricity 
copper wireThe LED module glowconduct electricity
♦ Do not operate a switch with a wet hand. Find out the reason behind it?
Water is a good conductor of electricity. When your hands are wet, the risk of electrical shock increases significantly. So, do not operate a switch with a wet hand.

♦ Conductors and Insulators 
• Conductors
Conductors are the substances that allow electricity to pass through them. Iron, gold, copper, steel, graphite and water are electric conductors. 

• Insulators 
Insulators are the substances that do not allow electricity to pass through. Dry wooden block, paper, plastic, cloth etc., are insulators. 
♦ Tabulate the situations were conductors and insulators are used.
Situations in which conductors are usedSituations in which insulators are used
• The copper wire through which electricity passes through 
• Aluminium/copper wire is used to conduct electricity in houses
• In electric devices, the part through which electricity passes is made of metals.
• Fuse wires are made of conductors.
• Plastic coating over copper wire 
• Insulation tapes are used while connecting the wires
• The part we touch on the switch is made of plastic.
• In electrical appliances, the outer part is made of insulators.


♦ Iron nail, copper wire, silver ornament, gold ornament, aluminium wire, a piece of zinc, lead wire, magnesium ribbon, a piece of tin sheet.

♦ Do all substances conduct electricity? 
Yes

♦ Do these substances have any common characteristics?
• They are all metals.
• All metals are conductors of electricity.

♦ Which metal do we normally use to transmit electricity through electric lines? 
Aluminum

♦ What is the reason for not using copper wire in electric lines?
Copper wire is not used for electric lines due to the following reasons:
• Copper is more expensive than aluminium
• Copper is denser and heavier than aluminium, making it more difficult to support and maintain, especially for overhead lines.
• Copper can corrode when exposed to air and moisture, which can reduce its conductivity and lifespan.
So Aluminum is a more practical choice for electric lines due to its lower cost, lighter weight, and corrosion resistance. 

♦ Find out the uses of each of the tools. 
• Cutting pliers - for cutting wire
• Stripper - stripping off insulation
• Screwdriver - tightening or loosening screws
• Tester - testing electric current

♦ Some commonly used symbols in circuits are given below
♦ Observe the given circuits.  Identify the parts marked A, B, C and D. 
• Circuit 1  
A. An unlit bulb 
B. Cell
C. Switch off mode
D. Conducting wire

• Circuit 2  
A. A glowing bulb
B. Cell
C. Switch on mode
D. Conducting wire

♦ What are the differences between the two circuits?
• Circuit 1  - Open circuit
• Circuit 2  - Closed circuit 

♦ We have used a 9 V battery to make an emergency lamp. Will we get an electric shock if we touch the wire connected to the battery?
No

♦ If, somehow the electricity used at home passes through our body, it can cause electric shock.  What is the reason?  
The electricity we use at home is 230 V. 

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♦ What is electric Shock? 
• We get an electric shock when electric current passes through our body.
• Our body is an electric conductor since water is present in the living cells.
• Electric shock occurs when a broken power line or an external electric source, like an uninsulated circuit comes into contact with the body.
• Sometimes this causes severe burns.  
• Cardiac arrest is the major reason for death due to electric shock. 

♦ Observe the given situations.  Find out the situations in which there is a chance for electric shock and put a tick mark (√ ) in the appropriate boxes.
Using devices of good
quality		  Removing the plug pin
without switching off		√
Changing bulb when the
switch is on		 √ Using wires without proper insulation√
Turning on a switch with
wet hand		 √ Repairing devices while
switches are turned on		√
Removing the fan from
the ceiling after turning the main switch off		  Using footwear while ironing clothes
♦ Find out the situations in which you are likely to get an electric shock?
Changing bulb when the switch is on
Turning on a switch with wet hand
Removing the plug pin without switching off
Using wires without proper insulation
Repairing devices while switches are turned on

♦ What are the precautions to be taken while handling electrical appliances?
• Always read the manufacturer’s instructions and safety guidelines before using any electrical appliance.
• Switch off and unplug appliances when not in use.
• Keep appliances away from flammable materials.
• Never handle electrical appliances with wet hands to avoid electric shocks.
• Regularly check the cords and plugs for damage. Do not use appliances with frayed cords or broken plugs.
• Always turn off and unplug appliances when they are not in use or before cleaning them.
• Keep electrical appliances out of reach of children
♦ What are the things to be done immediately to save a person who has suffered an electric shock? 
• The first thing to be done is to disconnect the electric contact. You can switch off or remove the fuse for this. If it is not possible, separate the person from the electric circuit using a dry wooden stick or some other good insulator.
• In the case of heart failure, perform chest compressions. Place one hand on top of the other and apply continuous pressure on the victim's chest. This should be done until the heart starts beating again.
• If breathing stops, give artificial respiration. Keep the body warm by massaging. 
• Take the person immediately to a hospital if the shock is severe. 

♦ Which fuel is used to operate a generator?
The generator produce electricity making use of energy from fuels like petrol, kerosene, diesel etc. 

♦ How do generators in a hydroelectric power station work?
Generators in hydroelectric power stations work using the energy obtained when water stored in reservoirs of dams falls from a height. 

♦ How is electricity generated in hydroelectric power stations?
• Generators in hydroelectric power stations work using the energy obtained when water stored in reservoirs of dams falls from a height. 
• In dams, water which is stored in reservoirs is carried through pipes and made to fall forcefully on to the turbines connected to the generators. 
• The force of falling water rotates the turbines. 
• The generators connected to the turbines start to work and produce electricity. • This electricity is transmitted to various places through electric lines.

♦ What are the different methods of electricity generation?
• Hydroelectric Power Station
• Thermal power station 
• Nuclear power station
• Windmill
• Solar panel

♦ A major part of the electricity produced in Kerala comes from which power plant?
The hydroelectric power station in Idukki.

♦ What is a Solar cell?
A solar cell is a device that converts solar energy into electrical energy. 

♦ What is a solar panel?
A solar panel is a combination of two or more solar cells. 

♦ What are the circumstances in which electricity is wasted?
• Bulb and fan switched on even when there is no one in the room.
• TV switched on even when there is no one to watch it.
• Bulbs switched on even during daytime.
• Refrigerator left open.
• Using outdated appliances that consume more electricity 
• Leaving devices on charge after they are fully charged.
• Chargers and electronic devices plugged in when not in use.

♦ What are the measures to prevent wastage of electricity?
• Turn off unnecessary lights and use natural light.
• Install LED lights
• Unplug electronic devices and chargers when not in use.
• Avoid using old electronic appliances.
• Buy Energy Star-rated appliance

Let’s Assess

1. What is the energy change in a battery when it is connected to an emergency lamp?
a.  Electrical energy changes into light energy
b.  Light energy changes into chemical energy
c.  Chemical energy changes first into electrical energy and then into light energy
d.  Chemical energy changes into electrical energy
Answer: c.  Chemical energy changes first into electrical energy and then into light energy

2. Of the following, which is in an open circuit?
a)  Rotation of fan
b)  A damaged bell is switched on
c)  Working of a mixie
d)  Glowing of a bulb
Answer: b)  A damaged bell is switched on

3. From where do the artificial satellites get electricity for its working?
a) Solar panel   
b) Diesel 
c) Petrol 
d) Coal 
Answer: a) Solar panel   
4. Sometimes there is power shortage in Kerala during summer season. Why?
• A major part of the electricity produced in Kerala is from the hydroelectric power stations.
• During summer, water levels in reservoirs and rivers decrease, reducing the capacity for hydroelectric generation.

5. A person is standing in water. An electric line breaks and falls into the water. Is the person likely to get an electric shock? Give reason.
• Yes, the person is very likely to get an electric shock. 
• Water is a good conductor of electricity. Electricity can travel quickly through the water, so it can cause an electric shock to anyone standing in or near the water.

6. Observe the diagram of an open circuit. Convert it to a closed circuit using appropriate symbols and draw it.

Answer:




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