Electric bell - class-VII
Description: electric bell | |
Number of Questions: 20 | |
Created by: Chandra Bhatti | |
Tags: current electricity and magnetism electric current and its effects effect of electric current electromagnetic forces electro-magnetism physics |
An electric bell has a resistance of $5 \Omega$ and requires a current of $0.25\ A$ to work it. Assuming that the resistance of the bell wire is $1 \Omega$ per $15m$ and that the bell push is $90m$ distance from the bell. How many cells each of emf $1.4V$ and internal resistance $2 \Omega$, will be required to work the circuit.
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$3$
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$4$
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$5$
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$Can't\ be\ determined$
Name one device that uses an electromagnet.
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Electric bell
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Barometer
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Lactometer
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All the above
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
Soft iron is used for making the armature of an electric bell because soft iron is magnetised easily on passing the current and completely demagnetised easily on withdrawing the current through the solenoid.
Working of electric bells is an example of
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Mechanical effect of electric current
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Heating effect of electric current
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Magnetic effect of electric current
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None of these
An electric bell contains an electromagnet, consisting of coils of insulated wire wound round iron rods. When an electric current flows through the coils, the rods become magnetic and attract a piece of iron attached to a clapper. The clapper hits the bell and makes it ring.
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
Striker is moved under influence of electromagnet when circuit is complete.
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 current flowing through the electromagnet
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None of the above
When the switch of electric bell is pushed,circuit completes and current flows leading an electromagnet to attract armature and ring the bell.
Which of the following is not a component of electric bell?
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Gong
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Ferromagnetic strip
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Low magnetic field permanent magnet to attract ferromagnetic strip
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None of the above
Electric bell works on the mechanism of electromagnets i.e, temporary magnets, and no permanent magnet is used.
Which of the following is a characteristic of a buzzer?
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It has different mechanism from electric bell.
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It has higher frequency of collision of gong and hammer
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It uses only AC power supply
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None of the above
In a buzzer, the simplest sort of doorbell, an electromagnet is used to operate a self-interrupting circuit. You can see how this system works in the diagram below. Click and hold the doorbell button to see how the buzzer works. ... This breaks the doorbell circuit, which shuts off the electromagnet.characteristic of a buzzer It has higher frequency of collision of gong and hammer
Which power supply can be used in electric bell
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$AC$
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$DC$
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Can't be predicted
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Both A and B
Electric bell works on the mechanism of electromagnets and for this any type of power either AC or DC can be used.
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 current flowing through the electromagnet
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Circuit is closed in the electric bell
When the switch of an electric bell is on then electric current in it :
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Flows and stops in succession
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Flows continuously
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First flows in one direction and after sometime in other direction
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Flows in beginning and then stops forever
The bell works on the principle of electromagnetism which says that when an electric current flows through the coil, the rods become magnetic and attract a piece of iron attached to a clapper. And the clapper hits the cap and comes back as the current stops, and hence the bell rings. So the current flows and stops in succession. And in this way the bell rings.
Why doorbell rings repeatedly when switch is pressed
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Because of nature of current
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Because electrical switch is built in such a manner
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Because of make and break arrangement
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Because of slight humidity in the circuit
Make and break arrangement causes striker to repeatedly hit the metal gong as long as switch is pressed. When Circuit is complete, electromagnet attracts the striker which hits metal gong. As soon as the striker moves, circuit breaks and electromagnet is inactive. Because of flexibility of striker, it moves back to its original position. As soon as it reaches original position, circuit is complete. This process repeats continuously.
What will happen if the strip in a doorbell loses its flexibility?
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Striker may break if current is large.
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After hitting the metal gong, it never returns to original position and only a single sound is produced.
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System of doorbell breaks
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Both A and B
Because of lack of flexibility, striker will resist change of motion more and may break if current is large.
What is the use of flexibility strip in a doorbell?
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It brings back striker to its original position
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It supports the motion of the striker
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It completes the electric circuit flexibly
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Its a safety precaution
Without the flexibility strip, the striker will not come back to original position when the electrical circuit breaks.
Electric doorbell
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Always consume power
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Consume power only when switch is pressed
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Do not consume power practically and needs only starting power
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cant say
When switch is pressed, circuit completes and ringing begins. Hence, electrical energy is converted to sound energy. As switch is released, no current flows and no energy is consumed,
Exposed Electric doorbell can be damaged by
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Mechanical damage
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High Electric currents
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Humidity
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All of the above
Mechanical Damage to metal gong or striker may hinder working of the bell.
During a doorbell ringing
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Current always flows in the circuit
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Electromagnet is always present
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Striker is always in contact with metal gong
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Striker always repeatedly hits metal gong
Striker repeatedly hits the metal gong when doorbell is ringing.
Armature is pulled towards the spring when it strikes the gong because
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The electromagnet gets demagnetized
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The current flow breaks
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Spring effect
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All of the above
The working of an electric magnet is based on the magnetic effect of current. When the key is pressed the circuit gets completed and current passes through it causing the electromagnet to get magnetized which in turn attracts the armature. This movement of the armature causes the hammer to strike the gong. However when the armature moves towards the gong the connection between the spring strip and adjusting screw is lost which breaks the circuit and the current flow is stopped thus demagnetizing the electromagnet. This causes the armature to return to its original position and it is thus pulled back due to the spring effect of the spring strip. This process is called a make and break circuit.
Which process is applied on a circuit for the working of an electric bell?
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Magnetization
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Make and break
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Both A and B
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None of the above
The working of an electric magnet is based on the magnetic effect of current. When the key is pressed the circuit gets completed and current passes through it causing the electromagnet to get magnetized which in turn attracts the armature. This movement of the armature causes the hammer to strike the gong. However when the armature moves towards the gong the connection between the spring strip and adjusting screw is lost which breaks the circuit and the current flow is stopped thus demagnetizing the electromagnet. This causes the armature to return to its original position and it is thus pulled back due to the spring effect of the spring strip. This process is called a make and break circuit.
The hammer hits the gong because
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It has electric charge
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It displays the spring effect
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It is attracted towards the electro-magnet
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All of the above
The working of an electric magnet is based on the magnetic effect of current. When the key is pressed the circuit gets completed and current passes through it causing the electromagnet to get magnetized which in turn attracts the armature. This movement of the armature causes the hammer to strike the gong.