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CBSE Questions for Class 7 Physics Electric Current And Its Effects Quiz 1 - MCQExams.com
CBSE
Class 7 Physics
Electric Current And Its Effects
Quiz 1
Choose the correct alternative which matches the second and third columns with the first column.
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$$(I)-(b)-(ii);\ (II)-(c)-(iv);\ (III)-(a)-(i);\ (IV)-(d)-(iii)$$
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$$(I)-(a)-(i);\ (II)-(b)-(iii);\ (III)-(c)-(iv);\ (IV)-(d)-(ii)$$
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$$(I)-(d)-(iii);\ (II)-(b)-(iv);\ (III)-(a)-(i);\ (IV)-(c)-(ii)$$
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$$(I)-(C)-(iv);\ (II)-(a)-(ii);\ (III)-(d)-(i);\ (IV)-(b)-(iii)$$
Explanation
(I) : A tap key is represented by the symbol (c) given in column II which is used to keep the circuit open.
(II) : An ammeter is
represented by the symbol (a) given in column II and is connected in parallel to the circuit.
(III) : A voltmeter is
represented by the symbol (d) given in column II and is connected in series to the circuit.
(IV) : A galvanometer
is
represented by the symbol (b) given in column II which is connected to the circuit to detect current.
In electric heater:
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Chemical energy is converted to electrical energy
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Electrical energy is converted to chemical energy
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Heat energy is converted to electrical energy
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Electrical energy is converted to heat energy
Explanation
When a current passes through an electric heater, it becomes very hot and becomes a source of heat. Therefore, in an electric heater, electrical energy is converted into heat energy.
A/an ............... is employed in an electric bell.
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steel bar
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electromagnet
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permanent magnet
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copper cylinder
Explanation
An
electromagnet
is employed in an electric bell.
When the push button is pressed the electric circuit is completed and the armature is attracted towards the electromagnet. As a result, the small spring gets detached from the screw due to which the electric circuit is broken and the electromagnet is demagnetized. Hence, the attraction disappears and the armature is brought back by the spring to its original position. Contact of the spring with the screw is now remade, which completes the electric circuit. The action is repeated over and over again continuously. The armature vibrates and the hammer attached to it strikes the gong and the bell rings and sound is produced.
When the switch of an electric bell is pushed
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Flow of the current stops through the electromagnet in the bell
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Current starts to flow through the electromagnet
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Voltage decreases in the circuit
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Circuit is closed in the electric bell
Explanation
When the switch of an electric bell is pushed
, the circuit is closed and the current starts flowing through the electromagnet in the bell & the bell starts ringing.
OPTION : B is correct
The longer line in the symbol of a cell denotes
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the positive terminal
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the negative terminal
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the direction of current
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all of these
Explanation
The longer vertical line in the symbol of a cell represents the positive terminal and t
he shorter line in the symbol of a cell represents the negative terminal
.
The shorter line in the symbol of a electric cell represents:
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The positive terminal
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The negative terminal
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The direction of current
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All of these
Explanation
The shorter, thicker vertical line in the symbol of a cell represents the negative terminal.
The longer, thinner vertical line in the symbol of a cell represents the positive terminal.
A rheostat is used in an electrical circuit
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to change the resistance of the circuit.
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to change the potential difference.
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to change the emf.
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to change the current through a particular instrument.
Explanation
A rheostat is a variable resistor which is used to control current. they are able to vary the resistance in circuit without interruption. the construction of a rheostat is very similar to potentiometer .Thus A rheostat is used in circuit to change the resistance of the circuit. so option correct is A.
Which of the following is the symbol for a bulb?
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0%
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Explanation
Option D represent symbol of bulb.
The figure given represents:
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switch in the 'ON' position
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switch in the 'OFF' position
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circuit breaker
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battery
Explanation
Correct Option is B.
Explanation for the correct answer :
The given figure represents the open circuit. Current do not flows in the circuit, and switch is said to be in OFF position.
When the two terminals of a battery are connected directly with a wire then:
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More electrical energy is stored in the cell
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The chemicals get used up very fast
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No current flows in the wire
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None of these
Explanation
When the two terminals of a battery are connected directly with a wire there will be a low resistance path for the current to flow. The wire will get heated a little bit (depends on the diameter of the wire less the diameter more heat) and the battery
will be quickly discharged. During depletion, it may become very hot, emit gasses, and possibly explode. The shorting wires will draw heavy current that may melt the wire or even cause them to soften and break.
Electric door bell employs
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Permanent Magnet
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Electromagnet
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Thermistor
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Electric bulb
Explanation
An electric bell is a mechanical or electronic bell that functions by means of an electromagnet. When an electric current is applied, it produces a repetitive buzzing, clanging or ringing sound.
Which of the following equipment does not work on principle of Joule's law?
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Electric Heater
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Electric Iron
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Electric Bulb
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Electric Fan
Explanation
The electric iron, electric heater and electric bulb are some of the familiar devices based on Joule’s Law, but electric fan is not based on Joule's Law. Thus option $$D$$ is correct.
The main function of a switch is to
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Allow charges of flow
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Complete or break a circuit
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Make the bulb glow easily
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Prevent electric shocks
Explanation
A switch is a device that is used for making and breaking electric current in a circuit. It is used to turn on and turn off daily used equipment like television, washing machine, fan, light, etc.
MCB stands for:
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Main circuit board
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Master code bill
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Miniature circuit breaker
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None of these
Explanation
MCB stands for Miniature circuit breaker.
What material is used for making the armature of an electric bell ? Give a reason for using this material.
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Soft Iron
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Carbon
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Glass
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Silicon
Explanation
Soft iron is used for making the armature of an electric bell because w
e don't want the armature to retain its magnetism when the current is withdrawn.
Soft iron is magnetised easily on passing the current and completely demagnetised easily on withdrawing the current through the solenoid.
The magnetic effect of electric current is used in a/an :
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electric motor
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geyser
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electromagnet
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electric bulb
An electric iron is based upon the principle of:
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Heating effect of current
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Magnetic effect of current
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Chemical effect of current
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None of these
Explanation
An electric iron is based on the principle of the heating effect of current.
When an electric current passes through a conductor (like a high resistance wire) the conductor becomes hot after some time and produces heat. This is called the heating effect of current.
Many devices such as.............. use batteries.
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Torches
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Transistors, toys
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T.V. remote controls
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All of these
Explanation
Torches
Transistors, toys
T.V remote controls
All of these use batteries.
The circuit breaker device which can be used in place of a fuse is called
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CBD
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MCB
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MCD
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CBF
Explanation
Answer is B.
Fuse boxes contain safety devices called fuses or circuit breakers - MCB (Miniature Circuit Breaker) which are designed to prevent an excess of electric current entering your house by only allowing a certain maximum current to flow in. When the electrical current is too large, an electromagnet attracts a spring loaded switch which breaks the circuit and cuts the power supply. The switch must be reset before any current can flow again.
Which device is voltmeter?
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Explanation
(a) : Ammeter
(b) : Galvanometer
(c) : Voltmeter
(d) : Bulb
Hence option $$C$$ is correct.
Symbol of open switch is:
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Explanation
(a) Closed switch
(b) Single-cell
(c) Open switch
(d) Voltmeter
Is the symbol for
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Ammeter
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Load
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Voltmeter
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None
Explanation
The symbol shown in the figure represents a switch.It is used to turn off or turn on the circuit.Thus option D is correct.
Symbol of closed switch is :
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Explanation
(a) Battery
(b) Closed switch
(c) Open switch
(d) Single cell
Choose the symbol of battery:
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Explanation
Option (a) : Cell
Option (b) : Battery
Option (c) : AC Source
Option (d) : Voltmeter
A battery is a combination of cells and hence is represented by a symbol showing multiple cells.
Hence, the correct option is B.
Which of the symbols in figure represent devices used to measure currents?
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(a) and (c)
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(a) only
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(a) and (b)
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(c) only
Explanation
Ammeter measures current.
(a) : Ammeter
(b) : Voltmeter
(c) : Galvanometer
Figure shows:
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Resistance and variable resistance
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Resistance and bulb
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Bulb and galvanometer
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Bulb and voltmeter
Match the columns
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1-d, 2-c, 3-b, 4-a
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1-c, 2-b, 3-d, 4-a
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1-a, 2-c, 3-d, 4-b
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1-b, 2-c, 3-d, 4-a
Explanation
The symbol shown in option 1 represents a load, that in option 2 represents a heater, in option 3 represents a bulb while in option 4 represents a resistance.
Option B
Which of the following shows ammeter?
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Explanation
(a) : Galvanometer
(b) : Ammeter
(c) : Single cell
(d) : Open switch
Choose the symbol of variable resistance:
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0%
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Explanation
According to options given
Option $$A\rightarrow$$ Fixed Resistance
$$B\rightarrow$$ Galvanometer
$$C\rightarrow$$ Variable Resistance
$$D\rightarrow$$ Bulb
Hence Option C
Symbol shown in figure represents.
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Voltmeter
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Ammeter
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Alternating current source
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Direct current source
Explanation
The symbol in the above figure represents an alternating current source.
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