TS 7th Class Science Important Questions 7th Lesson Electricity: Current and it’s Effect

These TS 7th Class Science Important Questions 7th Lesson Electricity: Current and it’s Effect will help the students to improve their time and approach.

TS 7th Class Science Important Questions 7th Lesson Electricity: Current and it’s Effect

Question 1.
Describe the construction of a dry cell.
Answer:
Construction of a dry cell.

• A dry cell consists of a container made up of zinc metal.
• This zinc container serves as the negative teminal in the centre.
• A carbon (graphite) rod with a metal cap serves as the positive terminal.
• The carbon rod is surrounded by a mixture of carbon particles and ammonium chloride.
• The cell is sealed from the top.

Question 2.
What is the reason for connecting electric bulbs in parallel in house hold electric circuit?
Answer:
If even a bulb fuses, the other bulbs continue to glow. Because a parallel circuit has more than one path for the flow of electricity.

Question 3.
Mention some electric appliances that get heated up when electric current passes through them.
Answer:

• Filament bulb
• Rice cooker
• Geyser
• Electric iron
• Hot plate
• Electric heater
• Welding iron
• Electric kettle
• Electric oven

Question 4.
Think of the main use of electrical appliances and write their names in the correct column.
Answer:

Used for	Used for heat	Used for a movement
1. Table lamp 2. Tube light 3. Filament bulb 4. A street lamp 5. An arc lamp 6. Vapour lamp	1. An electric kettle 2. A rice cooker 3. An electric oven 4. An electric iron 5. Geyser 6. Electric heater 7. Hot plate	1. A lift in a building 2. An exhaust fan 3. A cassette player 4. An electric mixer 5. A water pump 6. Electric motor 7. Electric fan

Question 5.
What is an ‘electric fuse’ ? How is it useful ?
Answer:

• A fuse is a small piece of wire. It is made of a special alloy that gets heated quickly and melts.
• If the current in the circuit is too high, the fuse wire gets heated and melts. This leaves a gap in the circuit. Automatically the circuit is broken and flow of electricity is stopped. This protects appliances from getting burnt due to the passage of a heavy current through them.

Question 6.
Are the cells used in torch light and wrist watch the same?
Answer:
No. Dry cells are used in a torch light. Button battery is used in a wrist watch. A watch battery or a button cell is a small single cell battery shaped as a squat cylinder typically 5 to 12 mm in diameter and 1 to 6 mm height.

Cells have a metal can forming the bottom body, with a circular insulated top cap. The can is the positive and the top cap is the negative terminal. Common cathode materials are manganese dioxide, silver oxide, carbon monofluoride, cupric oxide or oxygen from the air.

Question 7.
Write a few lines about MCB (Miniature Circuit Breaker)
Answer:
MCB is used in place of fuses. MCBs are switches which automatically turn off when current in a circuit exceeds the safe limit. k has a switch which goes OFF automatically if there is over heating. This breaks the circuit. If we turn them ON, the circuit is once again completed.

Question 8.
What does the term ‘one unit’ electricity mean?
Answer:
When any appliance of 1 kilowatt is used for one hour, it uses one kilowatt-hour (1 KWH) or ‘one unit’ of electricity.

Question 9.
The metre reading in my rent house in January is 400 units and in February 560 units. Calculate how much I have to pay towards electricity bill of February. Cost of 1 unit is ₹ 4.25.
Answer:
Reading in January = 400 Units
Reading in February = 560 Units
No. of units used = 560 – 400 = 160
Cost of each unit = ₹ 4.25
Total amount payable = 160 x 4.25 = ₹ 680/-

Question 10.
In a house there are six bulbs of 60 w each, six of 40 w each and three of 15 w each. All of them are used for 4 hours a day. How many units of electricity will be used up in 30 days? How much will they have to pay at 2.80/- per unit?
Answer:
Total power used = (6×60 W) + (6×40 W) +(3x15W) = 645w
Total power used per day = 645 W X 4 Hrs 2580 WH
But 1000 WH = 1KWH
∴ 2580 WH = \(\frac{2580}{1000}\) = 2.58 KWH
Power used in 30 days = 30 x 2.58 KWH = 77.4 KWH
Cost of the power ₹ 2.80 x 77.4 = ₹ 216.72

Question 11.
Expand LED.
Answer:
Light Emitting Diode

Question 12.
What are the positive and negative terminals in a dry cell?
Answer:
Carbon: +ve terminal; Zinc : – ve terminal.

Question 13.
How are the bulbs connected in our houses?
Answer:
In parallel.

Question 14.
How are the cells connected in a torch light?
Answer:
In series.

Question 15.
Which one has a filament in it ? – an ordinary bulb, LED, tube light?
Answer:
An ordinary bulb.

Question 16.
What is the material of a ‘fuse wire’?
Answer:
A low melting alloy.

Question 17.
1 unit’ of electricity means, what?
Answer:
1 KWH (1 Kilo Watt Hour)

Question 18.
Why do the bulbs glow brighter and brighter when the electric cells are connected in series?
Answer:
When electric cells are connected in series the same current flows through each bulb. So they glow brighter.

Question 19.
Why do the bulbs glow dim, when the electric cells are connected in parallel?
Answer:
When electric cells are connected in parallel, the current divides between the bulbs. So less current flows through each bulb. So the bulbs glow dim.

Question 20.
Do the electric bulbs using in your house glow with dry cell ? Why?
Answer: No.
Reason : A dry cell supplies current of a low voltage. But bulbs in the house require a current of high voltage to glow. Flame some questions on electricity and its influence in our day to day life.

• Why should we consider electricity is only the power to save us?
• Why are we inter linked our lives strongly with electricity?
• How does a man over come the scarcity of electricity in future?
• Electricity has become the strong part and parcel of our life. How can we say this?

Question 22.
Guess and write what happens to the fuse wire if the electric current flow though it exceeds a certain limit?
Answer:
If the current in the circuit is too high the fuse wire gets heated and melts. This leaves a gap in the circuit. Automatically the circuit is broken and flow electricity is stopped.

Question 23.
When a torch light is not working what questions do you pose to know the reason?
Answer:

• Why is torch light riot working?
• What may be the fault occured in the torch light?
• Which part is cause for not working torch light?
• Are there any linkings among the parts that led to the damage of torch?

Question 24.
We listen to radio or watch TV for weather forecast. What is the need of knowing weather forecast in day to day life?
Answer:
It is necessary to know the weather forecast for the following aspects.

• Farmers can plan their agricultural activities.
• Family members will plan to celebrate their functions.
• Some people can plan their journey to longer distances.
• People will make a plan to free from adverse atmospheric conditions.

Question 25.
How do you make an ‘electric cell’ ? Describe.
Answer:
We need a few things to make a cell.
Requirements :

• A discharged dry cell
• Injection bottles, sulphuric acid, a piece of thick copper wire, connecting wire, sand paper and a small knife.

Construction of a cell :

• Two 3 cm long bits of thick copper wire are cut, About 1 cm of the coating is scrapped off from both ends of these wires.
• The discharged dry cell is broken and opened. Its outer zinc metal covering is removed.
• From this zinc plate, two 2 mm and 3 cm zinc strips are cut.
• The copper wires and zinc strips are inserted separately into the rubber caps of the injection bottles.
• The copper wires and zinc strips should not touch each other.
• The zinc strip of one bottle is connected to the copper wire of the other bottle.
• Both the bottles are filled with sulphuric acid.
• The bottles are closed with the caps carrying copper wires and zinc strips. Now the cell is ready.

Question 26.
Write the materials used for making dry cell.
Answer:
Carbon powder, Ammonium chloride paste, zinc metal, polythene cover, carbon rod etc.

Question 27.
Complete the given table with relevant electrical home appliances that are used in our daily life.

Used for light	Used for heat	Used for movement
Eg : Table lamp

Question 29.
What are the symbols for the following electrical components?
Fuse, electric bulb ON, switch in OFF position, a plug key and a tap key.
Answer:

Question 30.
Why are standard symbols used, to represent electrical devices?
Answer:
A standard symbol conveys the exact meaning, with very few descriptions.

Question 31.
i. Indicate the sequence in which the cell, bulb and switch are connected in a circuit.
ii. Can you change the sequence and still make the circuit work?
Answer:
i. Positive terminal of the cell → Wire → Switch → Wire → Bulb → Wire → Negative terminal of the cell.

ii. Yes. We can change the position of the switch.
Positive terminal of the cell → Wire → Bulb → Wire → Switch → Negative terminal of the cell.

Question 32.
Draw the circuit diagram for the following parallel connection.

Answer:

Circuit diagram – Parallel Connection

Question 33.
How do we depend on Electricity and Electrical home appliances in our daily life?
Answer:

• The man became more dependent on electrical home appliances.
• People are interested in buying high technology electrical devices such as A.Cs, LED TVs,advanced technology washing machines, smart phones.
• Only because of the big revolution in the power generating system man deserves to procure all the material.
• Moreover man wanted to keep his / her life much comfortable by utilising advanced technology devices.
• Electricity one of the astonishing powers, creates many more sectors and at the same time brings the man to forget the physical work in day to day life.

Question 34.
Current is useful and at the same time it is dangerous also. What are the precautions to be taken regarding current?
Answer:

• Use quality switch hoards and copper wires.
• Use rubber gloves and rubber slippers while repairing the circuit wires.
• Do not use wet material while working with electrical appliances.
• Switch off the appliances after using them.

Choose the correct answer:

I. Conceptual Understanding

Question 1.
A dry cell converts ( )
A) Electrical energy into chemical energy
B) Chemical energy into electrical energy
C) Chemical energy into light energy
D) None of these.
Answer:
C) Chemical energy into light energy

Question 2.
A fuse wire is made of ( )
A) a high melting metal
B) platinum
C) a low-melting alloy
D) tungsten
Answer:
A) a high melting metal

Question 3.
I Kw = ………… Watts. ( )
A) 10
B) 100
C) 1000
D) 10,000
Answer:
C) 1000

Question 4.
symbol represents …….. ( )
A) cells in series
B) cells in parallel
C) bulbs in series
D) bulbs in parallel
Answer:
A) cells in series

Question 5.
Which lamp reduces wastage of electricity .. ( )
A) Incandescent
B) Flouroscent
C) CFL
D) None
Answer:
C) CFL

Question 6.
Unit of electricity is …… ( )
A) volt
B) ampere
C) watt
D) KWH
Answer:
D) KWH

Question 7.
Positive terminal of bulb is ……………. ( )
A) Zinc rod
B) Carbon rod
C) Copper wire
D) Ammonium chloride
Answer:
B) Carbon rod

Question 8.
In 1831 ……. invented dynamo first time. ( )
A) Michael Faraday
B) Joseph Priestly
C) Galileo
D) John Gutenberg
Answer:
A) Michael Faraday

Question 9.
The device used to close an electric circuit is …… ( )
A) Electric bulb
B) Battery
C) Switch
D) Fuse
Answer:
C) Switch

Question 10.
In the cell (battery) the container works as negative pole. ( )
A) Carbon
B) Plastic cap
C) Zinc
D) Ammonium chloride
Answer:
C) Zinc

II. Asking Questions and Making Hypothesis

Question 11.
If the circuit is open, then current ( )
A) flows
B) flow or may not flow
C) reverses
D) does not flow
Answer:
D) does not flow

Question 12.
When Asha switched on the bulb it did not glow. What do you think the reason could be? ( )
A) There is no power supply
B) Filament of the bulb may he broken
C) Fuse wire might be melted
D) All the above
Answer:
D) All the above

Question 13.
Choose the correct statement. ( )
A) Electric cell is a source of electric energy
B) There are no two terminals of an electric cell
C) The electric bulb has a fÌlarrìent that is not connected to terminals
D) 1 Kw = 100 Watts
Answer:
A) Electric cell is a source of electric energy

Question 14.
Find out the statement which is not true. ( )
A) Street light gives more heat
B) Lift takes passangers up and down
C) A rice cooker cooks rice
D) A tube light gives more light than a small bulb
Answer:
A) Street light gives more heat

III. Experimentation and Field lnvestigation

Question 15.
The device used as positive pole of the dry cell.
A) Carbon rod
B) zinc
C) dil. Hydrochloric acid
D) Sulphur
Answer:
A) Carbon rod

Question 16.
The simple cell that is prepared by our own ( )
A) A cell with dil. Nitric acid
B) A cell with dil. Sulphuric acid
C) A cell with chlorate solution
D) A cell with water
Answer:
A) A cell with dil. Nitric acid

IV. Information Skills and Project

Question 17.
Government advice to wide use of this type of bulb ( )
A) LCD
B) CFL
C) LED
D) A & B
Answer:
C) LED

Question 18.
World countries and India advise to mind generating power through ( )
A) Wind energy
B) Tidal energy
C) Solar power
D) All
Answer:
D) All

V. Communication through Drawing and Model Making

Question 19.
represents ( )
A) Switch
B) Battery
C) Fuse
D) Bulb
Answer:
C) Fuse

Question 20.
Find out the missing part in the diagram. ( )
Answer:
D)

Question 21.
The given symbol explains

A) Bulb in dim light
B) Bulb glows with bright light
C) Bulb does not light
D) Bulb damage
Answer:
B) Bulb glows with bright light

Question 22.
Cell Positive terminal → Wire → ? → Wire → Bulb → Wire → Cell negative terminal ( )
A) bulb
B) fuse
C) switch
D) M.C.B.
Answer:
C) switch

Question 23.
The electric circuit closed or opened can be identified with ( )

Answer:
B)

VII. Appreciation and Aesthetic Sense and Values

Question 24.
The dry cell based on the ‘Leclanche cell’ is widely used in ( )
A) Torches
B) Calculators
C) Radios
D) All of them
Answer:
D) All of them

Question 25.
The amount of heat liberated through the filament in an electrical appliance depends on ( )
A) type of wire
B) Thickness of wire
C) Nature of wire
D) Colour of wire
Answer:
C) Nature of wire

Question 26.
Modern fuse. ( )
A) Copper wire
B) Zinc piece
C) M.C.B.
D) Metal plate
Answer:
C) M.C.B.

Question 27.
Which is cheaper ( )
A) Electricity for domestic use
B) Electricity for commercial use
C) Electricity for domestic & Commercial
D) All the above
Answer:
A) Electricity for domestic use