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InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
People rely on magnets for industrial and commercial use. Since scientists began creating very strong magnets using electricity, magnets have become essential to the medical and electronic sectors. People even rely heavily on magnets in their homes. Briefly discuss three uses of magnets in different fields. |
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Answer» (i) Computes and Electronics. Every computer contains magnets for data storage on hard drives and to display images on computer screens. In electronics, the magnets guide electrons and metals to the appropriate place. (ii) Industry. Electric generators rely on magnets to convert mechanical energy into electricity, while some motors work in reverse. Electromagnetic cranes grab and move large amounts of metal. The maglev (magnetic leviation) trains operate using two opposing magnets that cause the train to float, making it extremely maneuverable and fast. (iii) Health and Medicine. Magnets are used in X-rays and MRI machines. |
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| 2. |
State two serious hazards of electricity. |
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Answer» 1. If a person accidently touches the live wire, he gets a severe shock which may prove fatal. 2. Short-circuiting or overloading can cause a spark which may lead to fire in a building. |
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| 3. |
What the two main precautions to be taken while using an electric supply? |
| Answer» Electric supply should be immediately switched off from the main switch in case a person touches a live electric wire or if there is a fire in the house. Electric supply should also be switched off during natural calamities like earthquakes, floods, etc. | |
| 4. |
Write the help of a labelled circuit diagram, describe an activity to illustrate the patterns of the magnetic field lines around a straight current carrying long conducting wire. (i) Name the rule that is used to find the direction of magnetic field associated with a current carrying conductor. (ii) Is there a similar magnetic field produced around a thin beam of moving: (a) alpha particles (b) neutrons? Justify your answer. |
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Answer» (i) Right-Hand Thumb Rule. (ii) (a) Yes as alpha particles being positively charged constitute a current in the direction of their motion. (b) No as neutrons being natural do not constitute a current. |
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| 5. |
What is the role of fuse, used in series with any electrical appliance? Why should a fuse with defined rating not be replaced by one with a larger rating? |
| Answer» A fuse used in series with an electric appliance limits the current through the appliance. Thus, it protects the appliance due to short-circuiting or overloading as when current exceeds the limit for which the fuse is rated, it blows off and the appliance is disconnected from the electirc supply. When a fuse with a defined rating for a particular appliance is replaced by one with larger rating, it does not blow off and the appliance is damaged due to larger current passing through it. | |
| 6. |
What is the capacity of an electric fuse used in (i) lighting circuit (ii) power circuit in house hold supply? |
| Answer» (i) 5A (ii) 15A. | |
| 7. |
Where do we connect a fuse: with live or with neutral wire? |
| Answer» We connect the fuse with live wire. | |
| 8. |
We use electromagnetic induction in many ways in our daily lives, in most cases without realizing it. One recent invention is a flashlight that works without a battery. Further, in air travel safety, electromagnetic induction is used to prevent dangerous metallic objects (such as knives and guns) from being carried on the planes. (i) When was electromagnetic induction discovered? To which human quality do you attribute this discovery? Visualize the scenario prior to this discovery. (ii) How does a batteryless flashlight work? (iii) How are passengers screened at the airport? |
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Answer» (i) Electromagnetic induction was discovered by Michael Faraday on 17th Oct, 1831 (just 186 years ago). Perseverance as Faraday had to struggle for six years to be successful in his endevour. There was no electricity (from generators) before that time. Life today is totally dependent on electricity, the eight wonder of modern civilized world. Look at the effects on our lives of a power failure lasting only a few hours and think of all the devices based on it: lights, radio, television, motors to drive the wheels of industry-the list is unending. (ii) As the flashlight is shaken, its internal permanent magnet passes through a coil, inducing a current. This current alternates in direction and thus needs to be turned into dc before it can charge a capacitor. Once the capacitor is fully charged, it can be used to create a current through a light-emitting diode (LED), which in turn gives off light, typically for several minutes. (iii) As a passenger walks through the arch of the airport metal detector, he is subjected to a series of magnetic field pulses. If he has a metal object on his person, the currents induced in the object create their own magnetic field "echo" that, when detected, gives the safety inspectors reason to check the passenger more thoroughly. |
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| 9. |
What important observation did Oersted make in his experiment with current-carrying conductors? |
| Answer» Around every current-carrying conductor, there is a magnetic field i.e., electricity and magnetism are linked to eath other. | |
| 10. |
Why is magnetic field maximum at the centre of a current-carrying coil? |
| Answer» Magnetic fields due to two semicircular segments of the coil assist each other at the centre. | |
| 11. |
What is the relation between a tesla, an ampere and a meter. |
| Answer» `1 tesla=(1 n ewt on)/(1 "ampere"xx1 "metre")`, i.e., `1T=(1N)/(1Axx1m)xx1N//Am`. | |
| 12. |
What is the advantage of the third wire of each connection in domestic appliances? |
| Answer» In case of a defect in any domestic appliances, current leaks to its body. The third wire of earth connection transfers this current to the earth. As a result of this, the user of the appliance is protected from the electric shock. | |
| 13. |
State whether the following statements are true or false.(a) An electric motor converts mechanical energy into electrical energy.(b) An electric generator works on the principle of electromagnetic induction.(c) The field at the center of a long circular coil carrying current will beparallel straight lines.(d) A wire with a green insulation is usually the live wire of an electric supply. |
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Answer» Correct Answer - False An electric motor converts electrical energy into mechanical energy. |
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| 14. |
What do you mean by magnetic flux? |
| Answer» The total number of magnetic field lines linked with a circuit is called magnetic flux. | |
| 15. |
What type of dynamo is used in a bicycle? |
| Answer» We use a DC dynamo in a bicyle. | |
| 16. |
What is the composition of the alloy Nipermag? |
| Answer» Iron, nickel, aluminium and titanium. | |
| 17. |
What type of current is given by a cell? |
| Answer» The currnet given by cell is DC. | |
| 18. |
Choose the incorrect statement from the following regarding magnetic lines of field:A. (a) The direction of magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points.B. (b) Magnetic field lines are closed curves.C. (c) If magnetic field lines are parallel and equidistant, they represent zero field strength.D. (d) Relative strength of magnetic field is shown by the degree of closeness of the field lines. |
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Answer» Correct Answer - C If the magnetic field lines are parallel and equidistant, they represent a uniform magnetic field. |
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| 19. |
What is the effect of inserting a soft iron core inside a current-carrying solenoid? |
| Answer» The magnetic field inside a solenoid becomes very strong (i.e., around 5000 times its value without soft iron core). | |
| 20. |
What is a solenoid? |
| Answer» A cylindrical coil is called a solenoid. | |
| 21. |
(a) How does the magnetic field (B) due to a straight conductor vary with distance (r) from it? (b) How does the magnetic field (B) vary inside a solenoid? |
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Answer» (a) B varies inversely as the distance (r) i.e. `Bprop1/r`. (b) B is uniform inside a solenoid. |
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| 22. |
The device used for producing electric current is called a:A. (a) generatorB. (b) galvanometerC. (c) ammeterD. (d) motor. |
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Answer» Correct Answer - A The correct option is (a) |
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| 23. |
(a) Which polarity is developed on the face of the solenoid when a north pole of a magnet is moving towards it? (b) Which polarity is developed on the same face of the solenoid when the north pole of the magnet is moved away from it? |
| Answer» (a) North pole. (b) South pole. | |
| 24. |
What type of dynamo is used in industry? |
| Answer» In industry, AC dynamo is used. | |
| 25. |
A coil of insulated copper wire is connected to galvanometer. What would happen if a bar magnet is (i) pushed into the coil? (ii) withdrawn from inside the coil? (iii) held stationary inside the coil? |
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Answer» (i) The magnetic flux linked with the coil changes (i.e., increases). As a result of this, an induced current flows in the coil and the galvanometer shows a momentary deflection (say towards right) i.e., the needle of the galvanometer moves momentarily in one direction. (ii) The magnetic flux linked with the coil changes (i.e., decreases). As a result of this, an induced current flows in the coil but in a direction opposite to that in case (i). Obviously, the galvanometer momentary shows a deflection in the opposite direction (i.e., towards left) i.e., the needle of the galvanometer moves momentary but in the opposite direction to (i). (iii) When the magnet is held stationary in the coil, there will be a magnetic flux in the coil but it will remain constant. Since the magnetic flux does not change, there is no induced current in the coil and the galvanometer shows no deflection. |
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| 26. |
How does a solenoid behave like a magnet? Can you determine the north and south poles of a current carrying solenoid with a help of bar magnet? Explain. |
| Answer» A current carrying solenoid behaves like a bar magnet and the polarities of its end depend upon the direction of current flowing through it. In order to determine the polarities of its ends, place it in a brass hook and suspend it with a long thread so that it moves freely. Bring north pole of a bar magnet near one of its ends. In case the solenoid moves towards the bar magnet, that end of the solenoid is a south pole and in case the solenoid moves away from the magnet, that end of the solenoid is its north pole. The polarity of the other end of the solenoid can similarly be determined. | |
| 27. |
(a) What is a natural magnet? (b) What is an artificial magnet? |
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Answer» (a) It consists of a number of oxides of iron with `Fe_3O_4` as its structural formula. (b) An artificial magnet is obtained when an iron or steel bar is rubbed against a natural magnet. |
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| 28. |
AB is a current-carrying conductor in the plane of the paper as shown in figure. What are the directions of magnetic fields produced by it at point P and Q? Given `r_1gtr_2`, where will the strength of the magnetic field be larger? |
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Answer» (i) Magnetic field is into the plane of the paper at P and out of it at the point Q. (ii) Since `Bprop1/r`, B at Q is greater than B at P as `r_1gtr_2`. |
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| 29. |
When is the force experienced by a current-carrying conductor placed in a magnetic field is largest? |
| Answer» The force experienced by a current-currying conductor is the maximum when the direction of current is perpendicular to the direction of the magnetic field. | |
| 30. |
What does the divergence of magnetic field lines near the ends of a current carrying straight solenoid indicate? |
| Answer» The divergence of magnetic field lines near the ends of a current-carrying solenoid indicates a decrease in the strength of the magnetic field near the ends (and beyond). | |
| 31. |
What is the relation between magnetic field (B), current (I) and distance (r) in case of a straight current-carrying conductor? |
| Answer» Correct Answer - `BpropI//r`. | |
| 32. |
State two ways by which the strength of an electromagnet can be increased. |
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Answer» (i) By increasing the number of turns in the winding on the soft iron core. (ii) By increasing the strength of the current through the winding. |
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| 33. |
State three factors on which the magnitude of the force on a current-carrying conductor placed in a magnetic field depends. Can this force be zero for some position of the conductor? |
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Answer» The magnitude of force (F) acting on a conductor of length (l) and carrying a current (I) when placed in a magnetic field of magnitude (B) depends upon I, l and B as follows: (i) `FpropI` (ii) `Fpropl` (iii) `FpropB`. No force acts on such a conductor when it is placed parallel to the direction of magnetic field. |
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| 34. |
State two ways by which the speed of rotation of an electric motor can be increased. |
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Answer» The speed of rotation of an electric motor can be increased by: (i) increasing the strength of the current, (ii) increasing the number of turns in the coil. |
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| 35. |
A DC motor is rotating in clockwise direction. How can the direction of rotation be reversed? |
| Answer» The direction of rotation of the motor can be reversed by reversing the direction of current through the coil. This can be achieved by interchanging the terminals of the battery connected to the brushes of the motor. | |
| 36. |
The convert an AC generator into DC generator:A. (a) split-ring type commutator must be usedB. (b) slip rings and brushes must be usedC.D. (d) a rectangular wire loop has to be used |
| Answer» Correct Answer - A | |
| 37. |
The essential difference between an AC generator and a DC generator is that:A. (a) AC generator has an electromagnet while a DC generator has permanent magnet,B. (b) DC generator will generate a higher voltage,C. (c) AC generator will generate a higher voltage,D. (d) AC generator has slip rings while the DC generator has a commulator. |
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Answer» Correct Answer - D The correct option is (d). |
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| 38. |
How is AC different from DC? |
| Answer» The direction and magnitude of AC change periodically whereas in case of DC, these remain constant. | |
| 39. |
(a) Which is more dangerous: AC or DC? (b) Why so? |
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Answer» (a) AC as it attracts a person to it. (b) The person attracted towards AC power line may receive a shock and may even be electrocuted. |
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| 40. |
(a) Can we use AC for electroplating? (b) Can we operate an AC electric motor using DC? |
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Answer» (a) No, DC is used for electroplating as AC keeps on changing its polarities. Electroplating requires fixed polarities. (b) No, the mechanism of operation of an AC motor is different from that of a DC motor. |
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| 41. |
In figure, how do we think the displacement of rod AB will be affected if (i) current in the rod AB is increased, (ii) a stronger horse-shoe magnet is used, and (iii) length of the rod AB is increased? |
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Answer» Force `(F)` acting on a conductor of length (l) carrying current (I) placed in a magnetic field `(B)` is given by `F=IlB` (i) If the current (I) in the rod AB is increased, F also increases. (ii) When a stronger horse-shoe magnet is used, B increases. On account of this F also increases. (iii) If the length (l) of the rod is increased, F also increases. |
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| 42. |
(a) Which force is independent of the state of rest or of motion of a charged particle: electric or magnetic? (b) Which of the two force is stronger: magnetic force or electric force? |
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Answer» (a) Electric force. (b) Electric force `(F_e)` is stronger than the magnetic force `(F_m)` as `F_e//F_m~~10^(25)`. |
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| 43. |
What are the magnetic lines of force? Give their important properties. |
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Answer» The properties of magnetic lines of force are as follows `to` Magnetic field lines emerge from the north pole. `to` They merge at the south pole. `to` The direction of field lines inside the magnet is from the south pole to the north pole. `to` Magnetic lines do not intersect with each other. |
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| 44. |
In figure 8, how do we think the displacement of rod AB will be affected if (i) current in the rod AB is increased, (ii) a stronger horse-shoe magnet is used, and (iii) length of the rod AB is increased? |
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Answer» The displacement of rod AB is increased due to magnetic force exerted on it, if : (i) If the current in the rod is increased then rod will be deflected with greater force. (ii) If a stronger horse-shoe magnet is used then also rod will be deflected with greater force due to the increase in magnetic field. (iii) If the length of the rod AB is increased. |
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| 45. |
What is the role of the split-ring in an electric motor? |
| Answer» With the help of split-ring commutator, the direction of the current through the coil gets reversed after every half rotation of the coil. Thus, the direction of rotating couple remains unchanged and the coil continues to rotate in the same direction. | |
| 46. |
What is the difference between the terms overloading and short-circuiting? Why are coils of electric heaters made of an alloy rather than a pure metal? |
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Answer» (a) (i) Short-circuiting occurs when a live wire comes in contact with a neutral wire. Overloading occurs when many electrical appliances of high power rating are operated at the same time. (ii) In short-circuiting, a large current flows through the circuit because the resistance of the circuit formed when two wires touch each other is very small. In overloading, a large amount of current is drawn from the electric supply due to use of many electrical appliances. (b) (i) The resistivity of an alloy is much higher than that of the pure metal. (ii) An alloy does not oxidise easily even at high temperatures. |
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| 47. |
State whether the following statements are true or false. (a) An electric motor converts mechanical energy into electrical energy. (b) An electric generator works on the principle of electromagnetic induction. (c) The field at the centre of a long circular coil carrying current will be parallel straight lines. (d) A wire with a green insulation is usually the live wire. |
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Answer» (a) False. An electric motor converts electric energy into mechanical energy. (b) True. (c) True. (d) False. A wire with a green insulation is usually the earth wire. |
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| 48. |
A current through a horizontal powerline flows in east to west direction. What is the direction of magnetic field at a point directly below it and a point directly above it? |
| Answer» The current is in the east-west direction. Applying the right-hand thumb rule, we get that the megnetic field (at any point below or above the wire) turns clockwise in a plane perpendicular to the wire. When viewed from the east end. and anti-clockwise. when viewed from the west end. | |
| 49. |
At the time of short-circuit, the current in the circuit:A. (a) reduces substantiallyB. (b) does not changeC. (c) increases heavilyD. (d) varies continuously. |
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Answer» Correct Answer - C The correct option is (c) |
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| 50. |
When does an electric short-circuit occur? |
| Answer» If the insulation of the wires used in the circuit is damaged or the appliance used is faulty due to which the live wire and the neutral wire comes in direct contact as a result current in the circuit rises and the short circuit occurs. | |