- ATo reverse the direction of current every half rotation.
- BTo provide electrical contact between the rotating coil and external circuit.
- CTo increase the magnetic field strength.
- DTo reduce power loss due to heating.
Slip rings provide continuous electrical contact between the rotating armature coil and the stationary external circuit (brushes) while allowing the coil to rotate freely. They do not reverse the current direction; that's the function of a commutator in DC generators.
More Questions on Magnetic Effects of Electric Current
1Why is the current in the neutral wire usually zero when all appliances in a domestic circuit are switched off?
→ 2A bar magnet is moved towards a coil of wire. What factors influence the magnitude of the induced current?
→ 3An electric motor's armature current is increased. What is the effect on its output mechanical power?
→ 4What kind of magnetic field is produced by a current-carrying circular loop at its center?
→ 5How does a fuse differ from a circuit breaker in terms of functionality and reusability?
→ 6What is the direction of the magnetic force on a straight current-carrying wire placed in a uniform magnetic field, if the current flows into the page and the magnetic field points from left to right?
→ 7Explain why it is not advisable to use bare wires for electrical connections in homes.
→ 8If a small coil is placed inside a large current-carrying solenoid such that their axes are parallel, and the current in the solenoid is gradually increased, will an EMF be induced in the small coil?
→ 9An electric current is flowing in a straight conductor from north to south. What is the direction of the magnetic field lines when viewed from a point directly below the conductor?
→ 10How does increasing the number of turns in the coil of an electromagnet affect its strength?
→ 11A copper rod is moved towards a solenoid with its North pole facing the rod. What is the direction of the induced current in the rod if any?
→ 12Why are some devices in domestic circuits connected to the earth wire?
→ 13Two straight, parallel conductors carry current in opposite directions. Describe the force between them.
→ 14A square loop of wire is moved into a uniform magnetic field, then through it, and finally out of it. Describe when an induced current will flow in the loop.
→ 15What is the primary function of a circuit breaker?
→ 16A permanent magnet is used in a galvanometer. What is the role of this magnet?
→ 17Which type of generator is used to produce electricity for most household and industrial purposes?
→ 18Why is it essential to use a low melting point material for a fuse wire?
→ 19What would be the effect on the magnetic field inside a solenoid if both the current and the number of turns per unit length are halved?
→ 20A wire of length L carrying current I is placed in a uniform magnetic field B. What is the condition for the force on the wire to be maximum?
→ 21Which of the following determines the direction of the magnetic field produced by a straight current-carrying conductor?
→ 22A transformer works on the principle of:
→ 23This makes sense.
→ 24A student places two bar magnets such that their North poles face each other at a small distance. Now, a current-carrying wire is placed exactly between them, perpendicular to the line joining the poles. If the current flows vertically upwards, what will be the direction of the force experienced by the wire?
→ 25If an electron beam is directed horizontally towards the north and enters a magnetic field pointing vertically downwards, what will be the direction of deflection of the electron beam?
→ 26A proton enters a uniform magnetic field directed into the page. If the proton's velocity is to the right, what is the direction of the magnetic force on the proton?
→ 27How does increasing the area of a coil affect the induced EMF in a generator, assuming other factors remain constant?
→ 28Why are circuit breakers often preferred over fuses in modern electrical installations?
→ 29Describe the working principle of an electric bell, relating it to the magnetic effects of current.
→ 30A copper wire is held between the poles of a magnet. If the wire is moved upwards, an induced current is observed. What happens if the wire is moved downwards with the same speed?
→ 31What will happen to the magnetic field lines around a straight current-carrying conductor if the current is increased?
→ 32Why is an AC generator more commonly used than a DC generator for power generation at power stations?
→ 33Explain how the direction of induced current can be predicted using Fleming's Right-Hand Rule.
→ 34Which of the following is not a property of magnetic field lines?
→ 35A compass needle is placed on a table. A current-carrying wire is brought directly above the compass needle. If the current flows from west to east, what will be the direction of deflection of the north pole of the compass?
→ 36Why does a motor usually have a cylindrical soft iron core inside its armature coil?
→ 37Consider a current-carrying wire bent into a circular loop. If the current flows clockwise, what is the direction of the magnetic field at the center of the loop?
→ 38What is the purpose of the insulated covering on electric wires?
→ 39Explain the term 'short-circuiting' in a domestic electric circuit and its potential hazards.
→ 40An electric fuse has a rating of 5A. Can it be used in a circuit that draws a maximum current of 7A? Justify your answer.
→ 41A strong bar magnet is dropped vertically downwards into a long, thick copper pipe. Describe the observed motion of the magnet and explain why.
→ 42Why are the pole pieces of an electric motor made concave?
→ 43Which of the following would NOT affect the strength of the magnetic field produced by a current-carrying straight wire?
→ 44A wire loop is moved away from a current-carrying solenoid. In which direction will the induced current flow in the loop, if the solenoid's current creates a North pole on the side facing the loop?
→ 45What is the primary difference in the internal structure of an AC generator compared to a DC generator?
→ 46Describe how a galvanometer can be converted into an ammeter.
→ 47Consider a scenario where a metal rod is dropped through a strong magnetic field. What phenomenon occurs, and what is its implication on the rod's motion?
→ 48Why is a fuse always connected in the live wire of an electric circuit?
→ 49What would happen if the brushes of a DC motor were made of insulating material instead of conducting material?
→ 50A beam of alpha particles (positively charged) is projected horizontally towards the east. If a uniform magnetic field exists vertically upwards, in what direction will the alpha particles be deflected?
→ 51Explain why two magnetic field lines never intersect each other.
→ 52A current-carrying solenoid is compressed, reducing its length while keeping the number of turns and current constant. How does this affect the magnetic field strength inside it?
→ 53A circular loop carries current in a clockwise direction. What is the polarity of the face of the loop when viewed from the front?
→ 54If a straight conductor carries current vertically downwards, what is the direction of the magnetic field lines when viewed from a point to the east of the conductor?
→ 55A student connects a bulb, a battery, and a switch in series. When the switch is closed, the bulb glows. Now, he brings a compass needle near the wire. What will he observe and why?
→ 56Why is AC preferred over DC for long-distance transmission of electric power?
→ 57What is the significance of the 'earthing' wire in domestic circuits?
→ 58Explain the phenomenon of 'overloading' in a domestic electric circuit.
→ 59Which safety device is designed to protect electrical appliances from high currents due to overloading or short-circuiting?
→ 60Why is it dangerous to touch a live wire with bare hands?
→ 61A conductor is moved in a magnetic field. In which direction must it be moved to induce maximum current?
→ 62Explain the difference between AC and DC current generated by a generator.
→ 63A generator converts mechanical energy into electrical energy. What is the fundamental principle behind its operation?
→ 64How can the speed of rotation of a DC electric motor be increased?
→ 65Why are the field lines inside a current-carrying solenoid nearly parallel to each other?
→ 66Describe the role of a split-ring commutator in a DC electric motor.
→ 67An electric motor converts electrical energy into mechanical energy. On what principle does it work?
→ 68Consider a current loop placed in a uniform magnetic field. Under what conditions will the loop experience a net force?
→ 69A coil of insulated wire is wound around a cylindrical cardboard tube. Will it behave as an electromagnet? Justify your answer.
→ 70Why is soft iron used as the core of an electromagnet, rather than steel?
→ 71A conductor is placed perpendicular to a magnetic field and a current is passed through it. If the direction of the current is reversed, what happens to the direction of the force experienced by the conductor?
→ 72A charged particle enters a uniform magnetic field at an angle to the field lines. Describe the path of the particle and explain the force acting on it.
→ 73How does the strength of the magnetic field inside a current-carrying solenoid change if the number of turns per unit length is doubled, keeping the current constant?
→ 74Two parallel wires carry current in the same direction. What type of force exists between them, and why?
→ 75A student observes that a current-carrying solenoid, when suspended freely, aligns itself in a particular direction. Explain why this phenomenon occurs.
→ 76A compass needle is placed near a current-carrying straight conductor. If the direction of current in the conductor is reversed, what will be the effect on the compass needle?
→ 77Which of the following is a key application where temporary magnetism is crucial?
→ 78A compass needle deflects when brought near a current-carrying wire because:
→ 79The force between two parallel current-carrying wires depends on:
→ 80What material is typically used to insulate the wire in an electromagnet coil?
→ 81The region where magnetic field lines are closest together indicates:
→ 82Which animal uses Earth's magnetic field for navigation?
→ 83A simple electric bell uses an electromagnet to:
→ 84If you reverse the battery terminals connected to an electromagnet, what happens?
→ 85The magnetic poles always exist in:
→ 86Why are electromagnets preferred over permanent magnets in devices like magnetic separation machines?
→ 87How does the Earth's magnetic field protect us?
→ 88The magnetic field produced by a current-carrying wire is directly proportional to the:
→ 89Which effect of electric current is responsible for the working of an electric fan?
→ 90The direction of the magnetic field lines inside a bar magnet is from:
→ 91The magnetic field lines inside a solenoid are concentrated, indicating:
→ 92What would happen if you used an insulator as the core for an electromagnet?
→ 93If a magnet is broken into two pieces, each piece will:
→ 94A galvanometer is a device used to:
→ 95For Class 8, which simpler concept is often used to describe the strength of a magnetic field qualitatively?
→ 96Which of the following is an example of a natural magnet?
→ 97What is the main characteristic that makes an electromagnet different from a permanent magnet?
→ 98In a DC motor, the carbon brushes are used to:
→ 99The magnetic effect of electric current was first observed by accident during experiments with:
→ 100What type of core would make the strongest electromagnet?
→ 101If you increase the current in an electromagnet, its lifting power will:
→ 102The pattern of magnetic field lines around a straight current-carrying wire is:
→ 103A device that uses the magnetic effect of electric current to make or break a circuit is called a:
→ 104Which of these components is found in an electric motor?
→ 105The North pole of a compass needle is actually attracted to what kind of magnetic pole?
→ 106An electromagnet is useful because it allows us to:
→ 107The magnetic field lines never intersect each other because:
→ 108The force experienced by a current-carrying conductor in a magnetic field depends on:
→ 109What is the effect of changing the direction of current in a wire on the magnetic field around it?
→ 110When current flows through a circular loop, the magnetic field lines are densest:
→ 111A solenoid with more turns of wire will produce a ____________ magnetic field for the same current.
→ 112If you wind a coil of wire around a soft iron core and pass current through it, what have you created?
→ 113The magnetic effect of electric current is used in:
→ 114Which of these substances is NOT used to make a magnet?
→ 115A current-carrying conductor produces a magnetic field that is ___________ to the direction of current.
→ 116What kind of energy transformation occurs in an electric bell?
→ 117The strength of an electromagnet can be increased by:
→ 118Which of the following is a common use of an electromagnet in homes?
→ 119A magnetic field can pass through:
→ 120What happens to the magnetic field lines near the poles of a magnet?
→ 121If a current-carrying wire is placed North-South, and current flows from North to South, what will be the direction of the magnetic field directly to the East of the wire?
→ 122Magnetic field lines point from which pole to which pole outside a magnet?
→ 123What happens if you try to make an electromagnet without an iron core, just using a coil of wire?
→ 124Which of these is a temporary magnet?
→ 125To hold a car door shut, a device sometimes uses an electromagnet. This is because:
→ 126When a compass needle is placed exactly at the center of a current-carrying circular coil, it will align:
→ 127An electric current produces a magnetic field. This field can be detected by using a:
→ 128How can you increase the strength of an electromagnet without adding more turns to the coil?
→ 129The magnetic field lines inside a current-carrying solenoid are generally:
→ 130The magnetic poles of an electromagnet are determined by the:
→ 131Which of the following is a disadvantage of a permanent magnet compared to an electromagnet?
→ 132When the current in an electromagnet is turned off, what happens to its magnetic field?
→ 133If an electromagnet is made with a steel core instead of a soft iron core, what would be the likely outcome?
→ 134What is the role of a commutator in a DC motor?
→ 135The principle on which an electric motor works is:
→ 136An electric motor converts:
→ 137The strength of the magnetic field produced by a current-carrying conductor depends on the:
→ 138When a current flows through a circular loop of wire, the magnetic field lines inside the loop are:
→ 139A magnetic compass is used to determine:
→ 140In the Right-Hand Thumb Rule, if the current flows upwards, the magnetic field lines will be in which direction?
→ 141Which of the following is essential for the operation of an electromagnet?
→ 142The magnetic field lines outside a current-carrying solenoid are similar to those of a:
→ 143What is the effect on the magnetic field inside a solenoid if an iron core is inserted?
→ 144The North pole of a compass needle points towards the Earth's:
→ 145The Earth itself acts like a giant:
→ 146What is the primary function of the switch in an electric bell circuit?
→ 147Which material would you choose to make a permanent magnet?
→ 148The poles of an electromagnet can be reversed by:
→ 149When current flows through a solenoid, it behaves like a:
→ 150A solenoid is essentially a:
→ 151Which of the following devices relies on the magnetic effect of current to operate?
→ 152In an electric bell, the hammer strikes the gong when:
→ 153What happens to the magnetic field strength of an electromagnet if the current passing through its coil is doubled?
→ 154The magnetic field lines around a straight current-carrying conductor are:
→ 155When an electric current flows through a wire, the magnetic field produced around it is in the form of:
→ 156Which property makes soft iron suitable for the core of an electromagnet?
→ 157What happens to a compass needle if you bring a strong electromagnet close to it with the current on?
→ 158A current-carrying wire placed in a magnetic field experiences a:
→ 159Which type of magnet is typically stronger and can be controlled?
→ 160A key difference between a permanent magnet and an electromagnet is that an electromagnet:
→ 161If you hold a current-carrying wire in your right hand with your thumb pointing in the direction of the current, your curled fingers indicate the direction of the:
→ 162The direction of the magnetic field lines around a straight current-carrying conductor can be found using the:
→ 163Large cranes in junkyards use electromagnets to lift heavy objects because:
→ 164How does an electric bell work using an electromagnet?
→ 165Which device uses an electromagnet?
→ 166An electromagnet loses its magnetism when:
→ 167Which of the following does NOT affect the strength of an electromagnet?
→ 168To make an electromagnet stronger, one can:
→ 169What material is commonly used as the core of an electromagnet?
→ 170What is an electromagnet?
→ 171The phenomenon where an electric current produces a magnetic field around it is called the:
→ 172What did Oersted observe when current flowed through a wire placed near a compass?
→ 173Who discovered that electric current produces a magnetic field?
→ 174The region around a magnet where its influence can be detected is called:
→ 175Which material is attracted by a magnet?
→ 176What happens to a compass needle when placed near a bar magnet?
→ 177Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?
→ 178When is the force experienced by a current–carrying conductor placed in a magnetic field largest?
→ 179List two methods of producing magnetic fields.
→ 180At the time of short circuit, the current in the circuit (a) reduces substantially. (b) does not change. (c) increases heavily. (d) vary continuously
→ 181Which of the following correctly describes the magnetic field near a long straight wire? (a) The field consists of straight lines perpendicular to the wire. (b) The field consists of straight lines parallel to the wire. (c) The field consists of radial lines originating from the wire. (d) The field consists of concentric circles centred on the wire
→ 182List the properties of magnetic field lines.
→ 183Why does a compass needle get deflected when brought near a bar magnet?
→ 184Define the term induced electric current.
→ 185State the effect of a magnetic field on the path of a moving charged particle.
→ 186Write the frequency of alternating current (AC) in India. How many times per second it changes its direction?
→ 187Explain why alternating current is preferred over direct current for transmission over long distances.
→ 188Define alternating current and direct current.
→ 189Mention the frequency of D.C that is given by a cell.
→ 190Alternating current has a frequency of 50 Hz. What is meant by this statement? How many times does it change its direction in one second? Give reason for your answer
→ 191Mention and explain the function of an earth wire. Why it is necessary to earth metallic appliances?
→ 192Fuse acts like a watchman in an electric circuit. Justify this statement.
→ 193List three methods of producing a magnetic field.
→ 194What precaution should be taken to avoid the overloading of the domestic electric circuit?
→ 195Electric appliances like electric -press, toaster, fans etc are connected to electric mains through three-pin plug. Why?
→ 196What is the function of an earth wire? Why is it necessary to earth metallic casing of electric appliances?
→ 197A current-carrying straight conductor is placed in the east-west direction. What will be the direction of the force experienced by this conductor due to earth’s magnetic field? How will this force get affected?
→ 198Why is the earth pin thicker and longer than the live and the neutral pins?
→ 199When does an electric short circuit occur?
→ 200When is the force experienced by a current-carrying conductor placed in magnetic field largest?
→ 201State the principle of an electric generator.
→ 202What is the role of the split ring in an electric motor?
→ 203State and define S.I unit of magnetic field?
→ 204What is an electromagnet? Write two uses of an electromagnet?
→ 205State the factors on which strength of magnetic field at a point due to a current carrying conductor depends?
→ 206What is electric fuse? Where is it connected in a circuit?
→ 207Name and state rule used to determine the direction of magnetic field produced around a straight conductor carrying current?
→ 208Why do not two magnetic field lines intersect each other?
→ 209Write two ways to induce current in a coil?
→ 210Why does a compass needle deflect when brought near a bar magnet?
→ 211State two properties of magnetic lines of force?
→ 212In Faradays experiment if instead of moving the magnet towards the coil we move the coil towards the magnet. Will there be any induced current? Justify your answer. Compare the two cases.
→ 213If field lines of a magnetic field are crossed at a point, what does it indicate ?
→ 214What is meant by magnetic field?
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