7th Standard Syllabus & Materials
7th Standard
Tamilnadu 7th Standard Maths T2 - தகவல் செயலாக்கம் Important Questions And Answers Study Material - QB365 Set B
NEW7th Standard
Tamilnadu 7th Standard Maths T2 - தகவல் செயலாக்கம் Important Questions And Answers Study Material - QB365 Set A
NEW7th Standard
Tamilnadu 7th Standard Maths T2 - வடிவியல் Important Questions And Answers Study Material - QB365 Set C
NEW7th Standard
Tamilnadu 7th Standard Maths T2 - வடிவியல் Important Questions And Answers Study Material - QB365 Set B
NEW7th Standard
Tamilnadu 7th Standard Maths T2 - வடிவியல் Important Questions And Answers Study Material - QB365 Set A
NEW7th Standard
Tamilnadu 7th Standard Maths T2 - இயற்கணிதம் Important Questions And Answers Study Material - QB365 Set C
Published on: 13/12/2019
Electricity
Download Tamil Nadu 7th Standard Science question papers, model tests, one-mark questions, important questions, and public exam papers in PDF format. Free study materials and answer keys for TN State Board students.
Questions + Answers key
Take MCQ Science Test1.
In which of the following circuits are the bulb connected in series?
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2.
Small amounts of electrical current are measured in milliampere (mA). How many milliampere are there in 0.25 A ?
2.5 mA
25 mA
250 mA
2500 mA
3.
In the circuit shown, which switches (L, M or N) must be closed to light up the bulb?
switch L only
switch M only
Switch M and N only
either switch L or switches M and N
4.
In the circuit diagram below, 10 units of electric charge move past point x every second What is the current in the circuit _______
10 A
1 A
10 V
1 V
5.
S.I. unit of Electrical conductivity of a conductor is -----------
6.
--------- is used to measure the electric current.
7.
One unit of coulomb is charge of approximately ------------ protons or electrons.
8.
The representation of the electric current is A.
9.
In a parallel circuit, the electric components are divided into branches.
10.
The fuse wire does not melts whenever there is overload in the wiring.
11.
Electron flow is in the same direction to conventional current flow.
12.
Fuse
13.
Circuit
14.
Switch
15.
Cell
16.
Name some devices that run using heat effect of electric current.
17.
Define fuse.
18.
Name the device used to generate electricity.
19.
Define electrical conductivity.
20.
Differentiate parallel and serial circuits.
21.
Define an electric current.
22.
Explain the construction and working of a dry cell.
23.
Explain the heating effect of electric current.
24.
Explain the construction and working of an Telephone.
25.
A student made a circuit by using an electric cell, a switch, a torch bulb (fitted in the bulb holder) and copper connecting wires. When he turned on the switch, the torch bulb did not glow at all. The student checked the circuit and found that all the wire connections were tight.
What could be the possible reason for the torch bulb not glowing even when the circuit appears to be complete?
1.
(b)
2.
(c)
250 mA
3.
(d)
either switch L or switches M and N
4.
(a)
10 A
5.
( )
Siemens/meter (S/m)
6.
( )
Ammeter
7.
( )
6.242 x 1018
8.
False.
The representation of the electric current is 'I'.
9.
True
10.
False.
The Fuse wire melts whenever there is overload in the wiring.
11.
False.
Electron flow is in the opposite direction to conventional current flow.
12.
Reset by hand, circuit becomes complete once again
13.
A complete path for the flow of an electric current
14.
Used to open or close a circuit
15.
A device which converts chemical energy into electrical energy.
16.
Electric bulb, geyser, iron box, immersible water heater are the devices that run using heat effect of electric current.
17.
Fuse is a safety device which is used in household wiring and in many appliances.
18.
Electric cell is the device used to generate electricity.
19.
Electrical conductivity is the measure of a material's ability to conduct an electric current. It is commonly represented by the Greek letter σ(sigma). The S.I Unit of electrical conductivity is Siemens/meter(S/m).
20.
| S.No | Porollel circuit | Series circuit |
| 1. | Connected by branches | Single loop connection |
| 2. | Bulbs brighter | Bulbs dimmer |
| 3. | Each bulb fully powered | Bulbs share power |
| 4. | All bulbs stay glow if one goes out | All bulbs go out if one goes out |
21.
The flow of electric charges constitute an electric current. An electric current is measured by the amount of electric charge moving per unit time at any point in the circuit
22.
(i) Dry cells are normaly used in small devices such as remote control for T.V., torch, camera and toys.
A dry cells is a portable form of a leclanche cell. It consists of zinc vessel which acts as a negative electrode or anode the vessal contains a moist paste of saw dusts saturated with a solution of ammonium chloride and zinc chloride. The ammonium chloride acts as an electrolyte.
(ii) Electrolytes are substances that become ions in solution and acquire the capacity to conduct electricity.
(iii) The purpose of zinc chloride is to maintain the moistness of the paste being highly hygroscopic. The carbon rod covered with a brass cap is placed in the middle of vessel. It acts as positive electrode or cathode.
(iv) It is surrounded by a closely packed mixture of charcoal and manganese dioxide (MnO2) in a muslin bag. Here MnO2 acts as depolarizer. The zinc vessel is sealed at the top with pitch or shellac. A small hole is provided in it to allow the gases formed by the chemical action to escape. The chemical action inside the cell is the same as in leclanche cell
23.
i) When an electric current passes through a wire, the electrical energy is converted to hear. In heating appliances, the heating element is made up of materials with high melting point. An example of such a material is nichrome (an alloy of nickel, iron and chromium).
ii) The heating effect of current of electric current has many practical applications.
iii) The electric bulb, geyser, iron box, immersible water heater are based on this effect.
iv) These appliances have heating coils of high resistance.
Factors affecting Heating Effect of current
1) Electric Current
2) Resistance
3) Time for which current flows
Electric Fuse:
Electric fuse is a safety device which is used in household wiring and in many appliances. Electric fuse has a body made of ceramic and two points for connecting the fuse wire. The fuse wire melts whenever there is overload of the current in the wire. This breaks the circuit and helps in preventing damage to costly appliances and to the wiring. In electrical devices, a glass fuse is often used. This is a small glass tube, in which lies the fuse wire.
24.
Telephone:
In telephones, a changing magnetic effect causes a thin sheet of metal (diaphragm) to vibrate. The diaphragm is made of a metal that can be attracted to magnets.
1) The diaphragm is attached to spring that is fixed to the earpiece.
2) When a current flows through the wires, the soft - iron bar becomes an electromagnet.
3) The diaphragm becomes attracted to the electromagnet
4) As the person on the other end of the line speaks, his voice cause the current in the circuit to change. This causes the diaphragm in the earpiece to vibrate, producing sound.
25.
1) The electric cell produce weak energy.
2) The bulb filament is broken. (dead)
3) The both wires are connected to the same terminal of the cell.
4) Battery or cell is dead.
7th Standard Syllabus & Materials
7th Standard
Tamilnadu 7th Standard Maths T2 - இயற்கணிதம் Important Questions And Answers Study Material - QB365 Set B
NEW7th Standard
Tamilnadu 7th Standard Maths T2 - இயற்கணிதம் Important Questions And Answers Study Material - QB365 Set A
NEW7th Standard
Tamilnadu 7th Standard Maths T2 - அளவைகள் Important Questions And Answers Study Material - QB365 Set C
NEW7th Standard
Tamilnadu 7th Standard Maths T2 - அளவைகள் Important Questions And Answers Study Material - QB365 Set B
Tamilnadu Stateboard 7th Standard Subjects
Tamilnadu Stateboard Standards
