Basic Science Solutions for Class 7 Science Chapter 7 Electricity are provided here with simple step-by-step explanations. These solutions for Electricity are extremely popular among Class 7 students for Science Electricity Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Basic Science Book of Class 7 Science Chapter 7 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Basic Science Solutions. All Basic Science Solutions for class Class 7 Science are prepared by experts and are 100% accurate.

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We need to apply voltage across a bulb to cause a current to flow through it.

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A bulb gets warmer than the wires because the filament of bulb is made up of tungsten which provides greater resistance to the current than the wires, which are good conductors. Higher resistance leads to production of more heat. Radiation of heat from this heated up filament causes the bulb to heat up.

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Deflection of magnetic needle on bringing it closer to a current carrying conductor shows that   a current-carrying conductor behaves like a magnet.

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Iron nails get magnetised when they are placed in a current-carrying coil.

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We use a soft iron core in an electromagnet so that the electromagnet loses its magnetism as soon as the current is switched off.

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Four devices that use the heating effect of current are an electric heater, an iron, a toaster and a bulb.

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Electromagnets are used in motors, cranes, telephones and electric doorbells.

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A circuit diagram refers to the representation of a circuit showing its components using standard symbols.

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(a) Cell
(b) Bulb
(c) Battery
(d) Switch

Symbolic representation of positive and negative terminals in the symbol of a cell -

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The amount of heat produced by an electric current depends upon the resistance of the conductor and the magnitude of the current. As the resistance of the conductor and the magnitude of the current increase, the heat produced by the electric current also increases.

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A bulb has a long and thin tungsten filament because tungsten offers high resistance to the flow of current, moreover the length of the tungsten filament adds to this resistance which makes the bulb glow due to the generation of more heat.

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Two problems associated with the heating effect of current are:
1. When electric current flows through a conductor, a part of the electrical energy is converted into heat energy. This causes wastage of energy.
2. The heat produced can cause fires by damaging the insulation on wires.

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Electromagnets are magnets that are produced by passing an electric current through a coil wound around a soft iron core.
Two properties of an electromagnet are as follows.
1. Its strength depends on the number of turns of its coil and the amount of current passing through it.
2. Its magnetism lasts only as long as a current passes through its coil.

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The electric resistance of a piece of a material is a measure of the hindrance or obstruction it creates to the flow of electric current.

The resistance of a piece of a material depends on two factors:
(a) Thickness of the material
(b) Length of the material

Electric resistance produces obstruction to the flow of electric current. Higher the value of resistance of a conductor, the lower the value of electric current that can flow through it and vice versa.

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A fuse is a safety device that opens an electric circuit when excessive current flows through it, threatening the wires to burn due to excessive heat and closes the circuit when there is no current flowing through it.

A fuse contains a special wire whose melting point is lower than those of other conductors in the circuit. When the current flowing through the circuit becomes excessive because of a short circuit or an overload, the wire of the fuse becomes hot and melts. This breaks the circuit and prevents any damage to the circuit.

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An electric bell consists of a hammer, metal strip, gong and switch. It is made up of a coil of wire wound on an iron piece that acts as an electromagnet when electric current is passed through it. It works on the principle of electromagnetism.

The hammer of the bell is attracted towards the electromagnet when the circuit is complete. Further, the circuit breaks after the hammer moves towards the electromagnet. When the circuit breaks, the electromagnet does not attract the hammer, and the hammer returns to its original position because of a spring effect. As the hammer goes back to its original position, it touches the metal connector and the circuit is complete again. This cycle continues till the switch is kept in the 'on' position.

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1. The greater the voltage across a device, the greater is the current through it.
2. The connections between components are represented by lines in a circuit diagram.
3. A long wire has a higher resistance than a short wire.
4. An overload is a condition in which a wire carries a current that is more than what is safe.
5. A closely wound length of wire is called a coil.

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(c) on its resistance and the voltage across it

The magnitude of a current flowing through a device depends on the resistance of the device and the voltage across it.

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(c) heater elements

Nichrome is used for making heater elements because it has high resistance.

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(a) 6

To make a battery of 9 volts, six cells of 1.5 V are needed.



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