Class 10th Physics unit 15 Question An Anwer On Newsongoogle By Bilal Articles

Explore comprehensive Class 10th Physics Unit 15 questions and answers in an insightful article by Bilal on Newsongoogle. Gain a deeper understanding of key concepts with Bilal’s expert analysis and explanations. Elevate your Physics knowledge with this valuable resource.

Q 1. How magnetic lines of force are formed in the straight current-carrying conductor?

Ans: When current passes through a conductor, a magnetic field is produced in the space around it. If the conductor is a straight wire, the lines of force of this magnetic field would be in the form of concentric circles. These lines of force can be traced on a piece of cardboard with the help of a compass needle.

Q 2. What is the Right-hand grip rule?

Ans: The right-hand grip rule: Grasp a wire with your right hand such that your thumb is pointed in the direction of the conventional (positive) current. Then curling fingers of your hand will point in the direction of the magnetic field.

Q 3. What do the Cross and Dot stand for?

Ans: A dot indicates that the current is directed out of the plane of the paper i.e. it is flowing towards us where as a sign of a cross would mean that the current is directed into the paper i.e. it is flowing away from us.

Q 4. Write down the rules to find the polarity of the solenoid.

Ans: Right-hand Grip Rule: if we grip the coil with our right hand by curling our fingers in the direction of the conventional current, our thumb will indicate the north of the coil.

Q 5. State Fleming’s left-hand Rule?

Ans: The direction of the force acting on the wire can be determined by Fleming’s Left-hand rule. According to this rule, stretch the thumb, forefinger, and middle finger of the left hand mutually at the right angle to each other. If the forefinger points in the direction of the magnetic field, the middle figure in the direction of the current, then the thumb would indicate the direction of the force acting on the conductor.

Q 6. When the force on the current-carrying conductor in a magnetic field is maximum and when it is minimum.

Ans: When the current-carrying conductor makes an angle of 90° with the magnetic field or it is perpendicular to the field, the force on it is maximum. If the conductor is placed along or parallel to the magnetic field, no force acts on the conductor.

Q 7. What is D.C. Motor?

Ans: D.C. Motor is a device that converts electrical energy into mechanical energy, which is utilized for different types of work.

Q 8. Describe the working principles of D.C. Motor

Ans: Working principles: when a current-carrying coil is placed in a magnetic field, it experiences a couple due to which the coil begins to rotate. A D.C motor operates on this principle.

Q 9. How can we make the coil of the D.C. motor rotate continuously?

Ans: The coil can be rotated continuously by reversing the direction of the current just as the coil reaches its vertical position. This reversal of current will allow the coil to rotate continuously. To reverse the direction of the current, the connection to the coil is made through an arrangement of brushes and a ring that is split into two halves, called a split ring commutator as shown. Brushes, which are usually pieces of graphite, make contact with the commutator and allow current to flow into the loop. As the loop rotates, so does the commutator. The split ring is arranged so that each half of the commutator changes bushes just as the coil reaches the vertical position. Changing bushes reverses the current in the loop. As a result, the direction of the force on each side of the coil is reversed and it continues to rotate.

Q 10. What is the function of split rings D.C. Motor?

Ans: Split rings connect the coil to the battery through carbon brushes. When the coil rotates between the pole pieces of a magnet, split rings keep current in the sides of the coil after every half cycle, so the direction of force is changed after every half cycle.

Q 11. How the total force acting on the armature can be increased?

Ans: The total force acting on the armature can be increased by: i. Increasing the number of turns on the coil ii. Increasing the current in the coil iii. Increasing the strength of the magnetic field iv. Increasing the area of the coil

Q 12. What is the function of carbon brushes in D.C. Motor?

Ans: Two carbon brushes are used to press slightly against the split rings using springs and give a continuous passage of current to the coil.

Q 13. Define electromagnetic induction.

Ans: The process of generating an induced current in a circuit by changing the number of magnetic lines of force passing through it is called electromagnetic induction.

Q 14. State Faraday Law of electromagnetic induction.

Ans: The value of the induction e.m.f is directly proportional to the rate of change of flux. Mathematically e.m.f = rate of change of magnetic flux ( d∅ dx)

Q 15. Define A.C generator.

Ans: A device that produces or generates an alternating e.m.f is called an A.C generator. A.C. generator converts mechanical energy into electrical energy.

Q 16. Write down the principle of the A.C. generator.

Ans: When a coil rotates in a magnetic field, the flux passing through it continuously changes. This change of flux induces an e.m.f in the coil. This is the principle on which the A.C. generator works.

Q 17. What is meant by magnetic flux? When it is maximum and minimum?

Ans: The number of magnetic lines of force passing through a certain surface is known as magnetic flux passing through that surface. It is maximum when the area is held perpendicular to the direction of magnetic lines and minimum when the area is held parallel to the direction of magnetic lines of force.

Q 18. Is it possible that a constant current flowing in a coil produces an induced current in another coil?

Ans: No, a constant current flowing in one coil cannot produce an induced current in another coil. To produce induced current in another coil, the current in the first coil must be changing continuously so that magnetic flux may pass through another coil.

Q 19. Define Mutual induction.

Ans: If a current is induced in a circuit due to a change of current in another circuit, this phenomenon is known as mutual induction. Unit: S.I unit of mutual induction is Henry.

Q 21. Define transformer.

Ans: This is an electrical device that is used to increase or decrease the value of alternating voltage.

Q 22. What do you know about the primary coil and secondary coil?

Ans: Primary Coil: The coil of a transformer in which the change in current produces induced current in another coil is known as the primary coil. Secondary Coil: the second coil of the transformer in which current is induced is known as a secondary coil.

Q 23. Define Step Down Transformer and Step up transformer.

Ans: Step-down Transformer: if the turns in the secondary coil are less than the number of turns in the primary coil (Ns < Np), then such a transformer is called a step-down transformer. It is used to decrease A.C. Voltage. Step-up Transformer: if the voltage applied to the primary coil is to be increased, the number of turns in the secondary coil would be larger as compared to several turns in the primary, (Np < Ns). Such a transformer is known as a step-up transformer.

Q 24. What is the function of the core in the transformer?

Ans: The iron core enhances the magnetic flux produced in the primary coil and the magnetic flux linked to the secondary coil through the iron core.

Q 25. State Lenz’s Law?

Ans: The direction of an induced current in a circuit is always such that it opposes the cause that produces it.

Q 26. Prove that Lenz Law is a manifestation of the law of conservation of energy. OR How does induce e.m.f relate to the conservation of energy?

Ans: Induce e.m.f and conservation of energy: if we apply the law of conservation of energy to electromagnetic induction, we realize that the electrical energy induced in a conductor appears from the kinetic energy of the moving magnet. We do some work on the magnet to bring it close to the solenoid. This work consequently appears as electrical energy is the conductor. This mechanical energy of our hand used to push the magnet towards or away from the coil results in electrical energy. Hence Lenz law is a manifestation of the law of conservation of energy.

Q 27. Why alternating voltage is stepped up at the generating station?

Ans: Electric power is usually generated at places that are far from the places where it is consumed. The power is transmitted over long distances at high voltage to minimize the loss of energy in the form of heat during transmission. As heat dissipated in the transmission cable of resistance R is I 2RT. Hence by reducing the current through the cable, power loss in the form of heat dissipation can also be reduced. So the alternating voltage is stepped up at the generating station.

Q 28. How voltages are stepping down?

Ans: High voltages are transmitted to the main sub-station. This voltage is stepped down and is transmitted to the switching transformer station or the city substation. At the city sub-station, it is further stepped down to 220V and supplied to the consumer.

Q 29. Why mains power is supplied as alternating current?

Ans: Transformers play an essential part in power distribution. Transformers work only with A.C. This is one reason why mains power is supplied as alternating current.

Q 30. What is an electromagnet?

Ans: Electromagnet: The magnetic effect of current is called electromagnet.

Q 31. What is a Relay Circuit?

Ans: Relay Circuit: a relay is an electrical switch that opens and closes under the control of another electrical circuit. The relay is used to control a large current with the help of a small current.

Q 32. Explain the working principle of the relay circuit.

Ans: Working principle of relay circuit: the 1st circuit (input circuit) supplies current to the electromagnet. The electromagnet is magnetized and attracts one end of the iron armature. The armature then closes the contacts (2nd switch) and allows the current to the electromagnet stop. Now the electromagnet loses its magnetism and the 2nd switch is opened. Thus the flow of current stops in the 2nd circuit.

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