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Electric bells are mechanical or electronic bells that use electromagnets to operate.
- The electric bell is one of the many devices we use in our everyday life.
- It is commonly used at railroad crossings, telephones, fire and burglar alarms, school bells, and doorbells.
- An electric bell consists of one or more electromagnets, which are made using a coil of insulated wire wound around an iron bar.
- When the current flows, the magnetic field of the electromagnet becomes active.
- The electromagnet attracts an iron strip armature with a clapper.
- A hammer attached to the armature strikes the gong of the bell and produces a sound.
Read Also: Wave Nature of Electromagnetic Radiations
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Key Terms: Electric Bell working, Electromagnet, Electromagnet working, Electricity and Magnetism, Magnetic field, closed-circuit, open circuit, electromagnetic core
Electric Bell
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An electric bell is a device that informs us when someone is waiting at our gate when they ring the bell.
- It is a simple electrical circuit that functions using an Electromagnet.
- Electric bells are designed to run on low voltages ranging from 5 to 24 V AC or DC.
- In most residential applications, the doorbell circuit is powered by a small bell-ringing transformer.
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Electromagnet
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Electromagnets are artificial magnets. Their magnetic properties depend on the flow of current through them.
- When electric current passes through these metals, a magnetic field is generated around them. This magnetic field helps them act like permanent magnets.
- However, as soon as the current is removed, the magnetic field stops and the metal loses its magnetic properties.
- The simplest example of an electromagnet can be a wire wound in a coil or a wire wrapped around a magnet or soft iron. When current passes through this wire, it can start acting like an electromagnet.
- The strength of this magnetic field depends on the number of turns in the coil and the current flowing through it. A greater number of turns or increased current, both create a stronger magnet.
Magnetic Field
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- Magnetic fields are vector fields that show the movement of the electric charges and currents in and around a magnet when under some magnetic influence.
- Such charges generally experience a force that is perpendicular to the original direction of their movement.
- The effect of a magnetic field at different points of a magnet can be observed by moving a magnet around a compass and noting the change in direction to which the compass was pointing.
- To see the magnetic fields clearly you can perform a simple experiment. Place a thin glass sheet on a bar magnet and sprinkle some iron fillings on it. The fillings will arrange themselves along the magnetic field of the bar magnet and you can observe them carefully.
Magnetic Field
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Closed Circuit
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An electric circuit that is properly connected at all points and that allows the current to flow through it is called a closed circuit.
- A closed circuit is comparable to a road that crosses a river via a bridge.
- A bridge allows your vehicle to go across a road, across a canal, and back again.
- Electrical energy (electrons) can flow and move in a closed circuit.
- A closed circuit has no interruptions that can stop the flow of power.
- A closed circuit is one that is complete and allows current to flow.
Open Circuit
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An electric circuit that breaks at some point and that current cannot flow through is called an open circuit.
- In an open circuit, the two terminals are disconnected.
- As a result, the continuity of the circuit is broken.
- Even though the electric current cannot travel across the circuit, a voltage drop exists between two terminals.
- Therefore, the current flowing through an open circuit is zero, yet the voltage is there (non-zero).
Circuit of an Electric Bell
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When the circuit of an Electric bell is complete the current in the circuit activates the electromagnet that attracts the ging that hits the bell to ring it.
The different parts of this circuit are:
- A U−shaped electromagnet facing an armature that is supported by a spring.
- The spring is connected to an adjustable screw.
- The armature and an iron hammer form the system that hits the gong. This hammer is allowed a to and fro movement according to the circuit.
- In a normal position, when the circuit is open, the armature is in constant contact with the screw.
- There are two terminals on either side of the battery. One of the terminals connects the coil to the spring. The other terminal connects the battery to the spring through the adjustable screw.
Working of the Electric Bell
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- When the switch is turned on, current flows through the circuit and the electromagnet.
- As the current moves through the electromagnet, it gets magnetized. Consequently, it attracts the armature.
- Following this, the hammer strikes the gong and produces the signature sound.
- When the hammer moved, the contact between the attached screw and the spring broke.
- Subsequently, the circuit once again becomes an open circuit.
- Thus, the flow of current through the circuit stops and the electromagnet gets demagnetized.
- Following this, the armature restores its position through the spring.
- Hence, the armature contacts the adjustable screw once again.
- Finally, the circuit is back to its original position to repeat the work when the switch is pressed again.
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Things to Remember
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- An electric bell is a simple electrical circuit that functions using an Electromagnetic to inform us when someone is waiting outside our gate.
- Electromagnets are artificial magnets that become magnetized when electric current flows through them.
- Magnetic fields are vector fields that show the extent of the magnetic influence of the metal.
- A connected electric circuit that allows current to flow through it is called a closed circuit.
- A disconnected electric circuit that does not allow current to flow through it is called an open circuit.
- The different parts of this circuit are a battery, switch, terminals, adjustable screw, armature, metallic strip, electromagnet, hammer and a gong.
- When the circuit of an Electric bell is complete the current in the circuit activates the electromagnet that attracts the ging that hits the bell to ring it.
Check Further: Electromagnetic Spectrum
Sample Questions
Ques. Name two devices that use the magnetic effects of current to work. (2 Marks)
Ans. There are two common devices that use the magnetic effects of electric current. These devices are a loudspeaker and an electric bell. Many loudspeakers follow the electromagnetic principle. In this device, when a time-varying current flows through the voice coil moves, it moves within the gap between a permanent magnet. An electric bell is a simple electrical circuit that uses an electromagnet to form sound.
Ques. What is an electromagnet? What are its different uses? (2 Marks)
Ans. An electromagnet is usually a soft iron piece that is converted into a magnet when we pass some current through the coil wound around the iron piece.
Electromagnets are used in the functioning of motors and generators.
Ques. What is an electric bell? (2 Marks)
Ans. An electric bell is a mechanical or electronic bell that uses an electromagnet to function. When an electric current is applied, a buzzing, clanging, or ringing sound is produced.
Ques. What is the magnetic field? (2 Marks)
Ans. A magnetic field is a vector field that explains the magnetic effect on moving charges, currents, and magnetic materials. A moving charge in a magnetic field is subjected to a force that is perpendicular to both its own velocity and the magnetic field.
Ques. What are the properties of the electromagnets? (5 Marks)
Ans. The following are the properties of electromagnets
- An electromagnet is constructed with a soft iron core.
- An electromagnet is temporary in nature.
- The strength of the magnetic field can be adjusted.
- By turning off the current, an electromagnet can be easily demagnetized.
- The polarity can be changed.
Ques. What is the working principle of an electric bell? (2 Marks)
Ans. Electric bell works on the principle of the magnetic effect of electric current. The electromagnets attract the soft iron armature, and when the striker strikes the gong, sound is produced.
Ques. What is electric current? (2 Marks)
Ans. The flow of charged particles, such as electrons or ions, moving through an electrical conductor or space is referred to as an electric current. It is defined as the net rate of charge flow through a surface.
Ques. How electric bell work? (5 Marks)
Ans. When the switch is turned on, an electric current travels through the coil, and the iron core works as an electromagnet.
- The hammer is attracted to the iron core.
- The hammer makes a sound when it strikes the bell. When the hammer moves towards the iron core, the circuit is broken at the screw contact.
- The iron core is no longer an electromagnet at this time.
- The spring action of the steel rod pulls the hammer back to its original position, and it then strikes the contact again to complete the circuit.
- The circuit is complete, and electricity runs through the coil once again, striking the bell once more.
- The operation is repeated, and a ringing sound can be heard as the hammer continues to strike the bell until the switch is released.
Ques. Name the main parts of an electric bell. (2 Marks)
Ans. The components of an electric bell are an electromagnet, an armature, a spring, an armature rod, a hammer, and a gong.
Ques. What are the magnetic effects of Electric current? (2 Marks)
Ans. Magnetic effects of Electric current are called electromagnetic effects. This refers to the effect in which when an electric current passes through a wire coil, it acts as a magnet. This is generally observed in an electromagnet that is a soft iron rod with a wire wrapped around it.
Ques. Explain the construction of an electric bell. (3 Marks)
Ans. The different parts of this circuit are an electromagnet facing an armature that is supported by a spring which is further connected to an adjustable screw. The armature and an iron hammer form the system that hits the gong. When the circuit is open, the armature is in constant contact with the screw. There are two terminals on either side of the battery. One of the terminals connects the coil to the spring. The other terminal connects the battery to the spring through the adjustable screw.
Ques. What is an electric circuit? (2 Marks)
Ans. An electric circuit is a connection of wires and electrical elements that provides a closed path so that electricity can pass between the two terminals of an electric cell. The bulb attached to the circuit glows only when current flows through the circuit. The bulb is attached to the circuit mainly to check and confirm the flow of current in the circuit.
Ques. Name one method that can be used to check the direction of the magnetic field in a current-flowing wire. (3 Marks)
Ans. Maxwell’s corkscrew rule also known as the right-hand thumb rule illustrates the direction of the flow of the magnetic field associated with any straight current-carrying conductor. It states that “Imagine that you are holding a current-carrying straight conductor in your right hand with your thumb pointing in the direction of the flow of current. Now, your fingers should wrap around the straight conductor in such a way that it matches the direction of the flow of the magnetic field lines.”
Ques. Why is soft iron preferred over other metals for the core of an electromagnet? (2 Marks)
Ans. The soft iron bar is used for a core because it is a metal that acquires magnetic properties when an electric current flows through the solenoid. Also, it loses these magnetic properties as soon as the flow of current stops. Further, it is ferromagnet and hence acquires these magnetic properties easily and can retain them for a longer time.
Ques. How can you create an electromagnet? (2 Marks)
Ans. Anyone can create an Electromagnet by wrapping a wire around an iron nail and then allowing current to flow through the wire. The electric field produced in the wire coiled around the nail produces a magnetic field around the nail. In some cases, depending on the intensity of the current and the number of coils, the nail can remain magnetized even when it is removed from within the wire coil.
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