DAV Class 7 Science Chapter 17 Electric Current and Its Effects Question Answer Notes
DAV Class 7 Science Chapter 17 Electric Current and Its Effects Question Answer Notes Solution by Expert Science Teacher. DAV Class 7 Science 17th Chapter Electric Current and Its Effects for Students of DAV Schools.
Lesson No 17
Electric Current and Its Effects
A.) Fill in the blanks
Answer: (1) electric, mechanical (2) electric, heat (3) nichrome (4) electric fuse (5) magnetic field, ON
B.) True or False
Answer: (1) False, it can produce both (2) true(3) True (4) False, it may cause an overload/load shedding (5) False, no it cannot.
C.) Tick the correct option.
1.) When electric current flows through a filament of electric bulb, the filament gives out–
Answer: both heat and light energy
2.) A fuse wire is a wire of-
Answer: low resistivity and low melting point.
3.) We are more likely to observe a strong magnetic effect with a-
Answer: current carrying circular coil of many turns wound on a soft iron core.
4.) A common household device, that uses an electromagnet in its working, is-
Answer: the electric bell
5.) A good electromagnet would-
Answer: act like a magnet when the current is ‘ON’ but would not do so when the current is ‘OFF’.
D.) Answer the following
1.) The bulb in the circuit shown in figure does not glow. Why? Redraw the circuit diagram by making the necessary changes in it, so that the bulb starts glowing.
In the given circuit we see that the switch is open which does not allow current to pass through it. Also the battery has only positive terminals.
2.) Name three practical devices based on the heating effect of current.
Answer: (i) Electric iron (ii) geyser (iii) Electric heater
3.) Write two special characteristics of the wire needed for making the ‘element’ of an electric heater.
1) High resistance: The wire used to make the element of an electric heater should have a high resistance in order to create a large amount of heat.
2) High heat tolerance: The wire should also have a high heat tolerance in order to be able to withstand the high temperatures generated by the electric heater.
4.) Give the meaning of the terms ‘short circuiting’ and ‘overloading’ in an electric circuit?
Short circuiting: Short circuiting happens when an important connection connects two places that are not intended to be linked. This can cause a sizable current to flow through the circuit, potentially damaging its components.
Overloading: Overloading occurs when more current is drawn from a circuit than it was designed to handle. This can cause components to overheat, resulting in a possible fire hazard.
5.) Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.
No, you cannot use an electromagnet to separate a pile of rubbish from plastic shopping bags. The magnetic field electromagnets produce can be used to attract and hold ferrous metals in place. Non-ferrous materials can be distinguished from iron, steel, and other ferromagnetic materials using this technique. The plastic bags could be easily detached from the metals and would not be affected by the magnetic field.
6.) State any three applications of an electromagnet.
1.) Door locks: To keep the door firmly closed, door locks frequently use electromagnets. A strong magnetic field is produced when an electric current flows through the electromagnet, drawing a metal plate inside the door and keeping it from opening.
2.) Electric motors: To produce rotational motion, electric motors use electromagnets. To turn a shaft that is attached to other gears or components, they first use coils of wire to create a magnetic field.
3.) Magnetic levitation: To lift and move heavy objects, magnetic levitation systems employ electromagnets. High-speed trains, medical scanners, and more utilise this technology.
2.) Name three practical devices based on the heating effect of current.
Answer: (i) Electric iron (ii) geyser (iii) Electric heater
3.) Write two special characteristics of the wire needed for making the ‘element’ of an electric heater.
1) High resistance: The wire used to make the element of an electric heater should have a high resistance in order to create a large amount of heat.
2) High heat tolerance: The wire should also have a high heat tolerance in order to be able to withstand the high temperatures generated by the electric heater.
4.) Give the meaning of the terms ‘short circuiting’ and ‘overloading’ in an electric circuit?
Short circuiting: Short circuiting happens when an important connection connects two places that are not intended to be linked. This can cause a sizable current to flow through the circuit, potentially damaging its components.
Overloading: Overloading occurs when more current is drawn from a circuit than it was designed to handle. This can cause components to overheat, resulting in a possible fire hazard.
5.) Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.
No, you cannot use an electromagnet to separate a pile of rubbish from plastic shopping bags. The magnetic field electromagnets produce can be used to attract and hold ferrous metals in place. Non-ferrous materials can be distinguished from iron, steel, and other ferromagnetic materials using this technique. The plastic bags could be easily detached from the metals and would not be affected by the magnetic field.
6.) State any three applications of an electromagnet.
1.) Door locks: To keep the door firmly closed, door locks frequently use electromagnets. A strong magnetic field is produced when an electric current flows through the electromagnet, drawing a metal plate inside the door and keeping it from opening.
2.) Electric motors: To produce rotational motion, electric motors use electromagnets. To turn a shaft that is attached to other gears or components, they first use coils of wire to create a magnetic field.
3.) Magnetic levitation: To lift and move heavy objects, magnetic levitation systems employ electromagnets. High-speed trains, medical scanners, and more utilise this technology.
E.) Answer the following questions.
1.) The same amount of current flows through the connecting wires and the bulb filament. However, it is only the filament that glows. Why?
The substance used to make the light bulb’s filament can resist the current flowing through it. As a result, power is released as radiation and light when the electrons strike the filament. On the other hand, since the wires are composed of a conducting substance, no energy is exchanged because the current moves through them without encountering any resistance.
2.) The brightness of light, emitted by a bulb, is observed to decrease when an electric heater is connected in series with it. Suggest the likely reason for this observation.
The voltage is decreasing across the entirety of the bulb because the immersion heater consumes more energy than it does. As a result, the bulb produces less strong brightness.
3.) The brightness of light, emitted by a bulb, is observed to decrease when an electric heater is connected in series with it. Suggest the likely reason for this observation.
The use of circuits energy by the electric heater, which lowers the power consumption given to the bulb and lessens the impact of the illumination it provides, is most likely to blame for this.
4.) A novice electrician, while carrying out some repairs in Sumit’s house, tried to put a piece of tungsten wire in a ‘fuse. Sumit’s father, on noticing this, stopped him from doing so. Give reasons as to why he did that.
- Tungsten filaments shouldn’t be used in fuses because they can’t survive the tremendous energy that an overheated may exert to pass through them.
- When exposed to high currents, tungsten wires pose a risk of electrical discharge as well as fire due to their great brittleness.
- The connection would probably overheat very quickly and potentially catch fire because tungsten has a particularly extremely high melting point.
5.) Draw a labelled diagram of an electric bell and explain its working.
Electric current is made to pass through the circuit as a result current flows through the electromagnet and its magnetism is activated. as a result the magnetism attracts the armature, it bends towards the electromagnet and finally strikes the gong. as soon as the current stops flowing the electromagnet loses its magnetism and the gong is repelled as a result it does not hit the gong constantly.
More Extra Questions for Preparation
Q.1.) Fill in the blanks.
1.) Nichrome is used for making wires.
2.)In an electric cell, chemical energy is converted into electrical energy.
3.)The metal filament of an electric bulb is made up of tungsten wire.
4.)The ‘melt down action’ of a fuse wire depends upon its current rating.
5.) Electric bell is a simple device based on the magnetic effect of current.
Q.2.) True or false.
1.)The ’melt down’ limit of the current, for a given fuse wire does not depend on its length.
Answer – True
2.) The wires may become overheated and this can even result in a fire.
Answer – True
Q.4. ) Answer the questions.
1.) Explain Heating effect of electric current.
Answer – when an electric current flows through the filament of an electric toaster, the wires of the filament soon become red-hot. It follows that a flow of current can produce heat. This is known as the heating effect of electric current.
2.) What does heat produced on wire depends on?
Answer – the heat produced, in a given wire depends on
(i) the strength of the current through the wire.
(ii) the nature of the material and the length and thickness of the given wire.
(iii) the time for which electric current flows through the given wire.
3.) Write forms of energy.
Answer – Heat energy, Light energy, sound energy, mechanical energy, magnetic energy and
electrical energy are some of the well known forms of energy.
4.) Where are electromagnets used for ?
Answer – Electromagnets are used in electric cranes, electric bells, loudspeakers, telephone diaphragms, etc.
5.) What does an electric bell consists of?
Answer – It consists of a gong, an electromagnet, a soft iron rod (armature) and a contact screw,
Q.5.) Define the following.
1.) Electric fuse.
Answer – An electric fuse is a safety device which is used to limit the current in an electric circuit.
2.) Magnetic effect.
Answer – When an electric current flows through a wire, it behaves like a magnet. This is known as the magnetic effect of current.
3.) Solenoid.
Answer – One end of the coil acts like a magnetic north pole while the other acts like a magnetic south pole, such a coil is called as a solenoid.
Q.6.) Choose the correct answer.
1.) Touching of wires leads to
a.) Overloading
b.) Short circuit
c.) Insulation break down
d.) None of these
Answer – b. Short circuit
2.) The ‘melt down action’ of a fuse wire depends upon its
a.) Current rating
b.) Nature of material used
c.) Both a and b
d.) Current rating
Answer – a. Current rating
4.) a safety device used to limit electric current in an electric circuit.
a.) Electric bell
b.) Electric fuse
c.) Electro magnet
d.) All of these
Answer – b. Electric fuse
5.) Nichrome is used for making wires of heating coils because .
a.) It has a high melting point
b.) It has a high resistivity
c.) It can remain red hot for a long time without getting oxidised or burning out.
d.) All of these
Answer – d. All of these