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CBSE Questions for Class 6 Physics Electricity And Circuits Quiz 3 - MCQExams.com
CBSE
Class 6 Physics
Electricity And Circuits
Quiz 3
Electric current cannot flow through
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Silver
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Wood
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Copper
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None of these
Explanation
Wood is an insulator and hence does not allow electric current to pass through it.
Answer-(B)
State whether given statement is True or False
Silk threads are very good conductors.
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True
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False
Explanation
Silk threads are bad conductor electricity. so it allows less amount of current at high voltage applied.
Given statement is $$False$$.
State whether given statement is True or False
All electric appliances work only-if the circuit is complete.
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True
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False
Explanation
To operate electrical appliances electrical current in it required. and this current flow only when the circuit is closed or completed.
hence Given statement is true.
The path along which electric current flows is called
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electric circuit
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insulator
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conduct
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resistor
Explanation
An
electric circuit
is a path in which electrons from a voltage or current source flow. The point where those electrons enter an
electrical circuit
is called the "source" of electrons. The point where the electrons leave an
electrical circuit
is called the "return" or "earth ground".
The components required to make a simple series circuit to light a bulb are
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Wires and cell
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Cell and switch
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Bulb and wires
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Both B and C
Explanation
The component required to make a simple series circuit to light a bulb are
$$\rightarrow$$ Cells
$$\rightarrow$$ Switch
$$\rightarrow$$ Bulbs
$$\rightarrow$$ Wires
Why are switches/keys used in a circuit?
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To save power
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To protect the system
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To control a device
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All of above
Explanation
Switches allow the user of gadget to turn off the gadget when not required. Hence, A and C follows.
Using a device only when required reduced the wear and tear and protects the system. Hence, B is correct. hence A , b and C all are correct that's why option D is answer.
In an open electric circuit
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the path of electric current is completely broken
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the path of electric current is not broken
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the path of electric current is partially broken
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none of these
Explanation
An
electric circuit
in which the normal path of current has been interrupted, by the disconnection of one part of its conducting pathway from another, is called open electric circuit.In open circuit the path for current is completely broken or incomplete because current only flows in closed path.
When the circuit is open the electric current does not flow through it.
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True
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False
Explanation
The electric circuit provides a complete path for electricity to pass (current to flow) between the two terminals of the electric cell. When the circuit is open the electric current does not flow through it.
In a circuit having one bulb, another bulb is added in series with another. Then the
bulbs will :
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Not glow
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glow but less brigtly
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glow more brightly
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get fused
Explanation
The relation between the brightness and the current is $$Brightness\propto\ Current$$
In a circuit, if one more bulb is added in series with the other, the net resistance of the circuit increases, and hence the current decreases.
Hence the bulbs will glow but less brightly.
The substance which allows electric current to flow through it is called
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Conductor
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Insulator
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Semiconductor
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None of these
Explanation
The substance which allows electric current to pass through it are called $$conductor.$$
Answer-(A)
State True or False :
Two electrical circuits are always independent of each other.
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True
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False
Explanation
Consider the given circuit. It can be seen as combination of two circuits:
1. $$V_S$$ and $$R_1$$
2. $$V_S$$ and $$R_2$$
$$I_T$$ is common in both the circuits but dependent on the values of both $$R_1\ \text{and}\ R_2$$.
Human body is a
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good conductor of electricity
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poor conductor of electricity
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semiconductor
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good insulator
Explanation
Human body is a good conductor of electricity which allow electric current to flow.
Answer-(A)
What is false in an ideal Electrical Circuit?
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Internal Resistance of battery is zero
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Resistance of connecting wires is zero
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Wires are heated
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EMF of cell remains same
Explanation
In an ideal Electrical circuit, the conducting wires do not offer any resistance, i.e. $$R=0$$. From Joule's heating law: $$H=i^2Rt$$. Since $$R=0$$ therefore $$H=0$$. Thus, the complete electrical power from the source is delivered to the load and there is no loss of energy in the form of heat.
The heating of wires signifies energy lost as heat and is not a property of the Ideal Electrical Circuit.
Which of the following is false about fuse?
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A fuse controls the current that flows to the appliance.
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A fuse increases the resistance in the circuit to minimize the current flow.
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A fuse allows high current to flow through the circuit without damaging the appliance.
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A fuse protects the wiring and the appliance in the circuit from overheating.
Explanation
A fuse is usually a thin piece of wire that will melt and break the circuit if too large a current flows through it. The thicker the wire the more current is needed to melt it and the higher the 'rating' of the fuse. The purpose of a fuse is to protect the wiring and the equipment from getting high current.
Conducting wires in a circuit are usually made up of
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Copper
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Iron
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Magnet
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Fiber
Explanation
$$Copper$$ being good conductor and cheaply available are used as conducting wires in circuit.
Answer-(A)
Why is a fuse used in an electrical appliance?
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To earth the appliance
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To protect the appliance and its cable
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To change the efficiency of the appliance
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To change the current rating of the appliance
Explanation
An electric fuse is a safety device used to limit the current in an electric circuit. The use of a fuse is to safeguard the electric circuit and the electric appliances connected in the electric circuit from being damaged.
Which of the following devices can be used to break an electric circuit:
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Cell
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Bulb
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Switch
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None of these
Explanation
The switch is a simple device that is used to either break the electric circuit or
to complete it.
Look at the given figure. It consists of a cell, a bulb with the two terminals X and Y and wires with ends P and Q; and S and R. The direction of current will be
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PQRS
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SRQP
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PRQS
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SQRP
Explanation
The direction of current will be PQRS because the current flows from positive terminal of the cell to the negative terminal.
The bulb fuses because of _________ of ________ wire.
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Melting, filament
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Boiling, filament
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Melting, circuit
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Boiling, circuit
Explanation
The bulb produces light by a filament wire that gets heated by electric current and fuse when that filament wire melts due to overheating. So
the bulb fuses because of melting and filament wire.
Why the filament of bulb glows ?
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Excess of electricity passing through bulb filament, hence it glows
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Current passes through the filament, it gets heated up and become red hot, hence glows
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Current passing through filament cools it down, hence it glows
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None of these
Explanation
A filament has a lot of resistance to electricity. Therefore as a result of this, the filament heats up and become red hot and starts glowing, converting electrical energy to light energy. This is because of the Joule-effect, which means that resistances heat up when the electrical current runs through them.
When excess electricity passes through the bulb, what will happen to the bulb?
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Fuses
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Filament of bulb breaks up
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Glass of bulb breaks
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Filament of bulb get fired
Explanation
When excess electricity passes through the bulb,the bulb gets fuse. Since fuse is a piece of wire of materials with a very low melting point and the filament of the bulb breaks up because of overheating.
Identify the closed circuit
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Explanation
Closed circuit is a complete electrical connection around which current flow. Current flow from positive to negative terminal of the battery. As option D is a closed circuit and bulb is glowing, it is the correct option.
In option A, the insulated handle of the screwdriver won't let the current flow.
In option B, the two cells are not connected properly.
In option C, the switch is open so current won't flow.
Choose the closed circuit from the following options
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Explanation
The key is metal hence conduct the electricity Hence it is a closed system. In other options, there is some break or connection with nonconducting metal.
In following circuit the bulb will not glow if ends A and B are connected with ?
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Steel clip
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metal clip
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plastic clip
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copper wire
Explanation
The bulb will not glow if ends A and B are connected with plastic clip because plastic is a poor conductor of electricity and it does not allow electricity to pass through it. Whereas, Steel clip, Metal clip as well as Copper wire conducts electricity through them
Seema went to Usha's house to complete the project work given in school. Both were working on the project and suddenly the light bulb fuses. What could be the possible reason of fuse of bulb?
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Electricity Failure
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Breaking of filament of bulb due to overloading
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Breaking of fuse wire
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None of these
Explanation
An electric bulb may fuse due to many reasons. One reason for a bulb to fuse is a break in its filament. A break in the filament of an electric bulb means a break in the path of the current between the terminals of the electric cell.
When excess electricity or too much current passes through the circuit, it causes overheating and because of overheating the filament wire of bulb melts and then bulb gets fuse.
This is the reason why suddenly the light bulb fuses while Seema went to Usha's house to complete the project work given in the school.
Which of the following circuits will the bulb glow?
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Explanation
In figure (A), both ends of the bulb are connected to the negative terminal of the cell. So, bulb will not glow while in figure (B) and (C), insulating objects like string and rubber band are used. So, the circuit is incomplete and bulb will not glow. Figure (D) represents the complete circuit with proper connection. Hence, the bulb glows in figure (D).
Observe the given figure and answer the following questions. The bulb will glow when a ______ is placed in between the probes.
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Crayon
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Comb
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Key
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Piece of stone
Explanation
Materials that allow electric current to pass through them are called conductors.
Key is a metallic object. When it is placed in between probes then the current can easily flow in the circuit.
To flow current in the circuit, one need a
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Closed Circuit
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Source of potential difference
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Both A and B
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Neither A nor B
Explanation
To flow current through any circuit, Circuit need to be close and source of potential difference ie battery.
Hence option C.
A $$100$$W bulb $$B_1$$ and two $$60$$W bulbs $$B_2$$ and $$B_3$$, are connected to a $$250$$V source, as shown in figure. Now $$W_1$$, $$W_2$$ and $$W_3$$ are the output powers of the bulbs $$B_1, B_2$$ and $$B_3$$, respectively. Then.
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$$W_1 > W_2 = W_3$$
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$$W_1 > W_2 > W_3$$
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$$W_1 < W_2 = W_3$$
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$$W_1 < W_2 < W_3$$
Explanation
$$\therefore R_1 = \dfrac{V_1^2}{100}, R_2 = \dfrac{V_2^2}{60}, R_3=\dfrac{V^2}{60}$$,
$$W_1 = \dfrac{V_1^2}{R_1} = \dfrac{V^2R_1}{(R_1 + R_2)^2}$$,
$$W_2 = \dfrac{V_2^2}{R^2} = \dfrac{V^2R_2}{(R_1 + R_2)^2}$$
and $$W_3 = \dfrac{V^2}{R_3}$$
$$W_3 : W_2 : W_1 = \dfrac{(250)^2}{R_3} : \dfrac{(250)^2R_2}{(R_1 + R_2)^2} : \dfrac{(250)^2}{(R_1 + R_2)^2}R_1$$
or $$W_3 : W_2 : W_1$$.
$$= \dfrac{(250)^2}{V^2} \times 60:\dfrac{(250)^2}{\left[\dfrac{1}{100}+\dfrac{1}{60}\right]^2V^4} \times \dfrac{v^2}{60} : \dfrac{(250)^2V^2}{\left[\dfrac{1}{100} + \dfrac{1}{60}\right]^2V^4 \times 100}$$
or $$W_3 : W_2 : W_1$$
$$= 60 : \dfrac{100\times 100\times 60 \times 60}{160\times 160\times 60} : \dfrac{100\times 100\times 60 \times 60}{160\times 160\times 100}$$
$$= 64: 25: 15$$
Hence, $$W_1<W_2<W_3$$
Hence, the correct option is $$(D)$$
In the circuit shown in figure bulb will become suddenly bright if:
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contact is made or broken
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contact is made
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contact is broken
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Would not become bright
Explanation
When a circuit is broken$$,$$ the induced $$e.m.f$$ is largest$$.$$
Hence,
option $$C$$ is correct answer.
When
contact is broken, current
in the circuit
decreases. To oppose this inductor releases current and emf is induced. This induced emf is having high value hence
bulb will become suddenly bright
.
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