NCERT Class X Science Class: Chapter –13. Magnetic Effects of Electric Current – Part-5

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Question 20:

What does the divergence of magnetic field lines near the ends of a current carrying straight solenoid indicate?


The divergence (degree of closeness) of magnetic field lines near the ends of a current carrying straight solenoid indicates a decrease in the strength of the magnetic field near the ends of the solenoid.

Image A solenoid

Image a Solenoid

Question 21:

Name four appliances wherein an electric motor, a rotating device that converts electrical energy to mechanical energy, is used as an important component. In what respect motors are different from generators?


The four appliances such as electric fans, washing machines, mixers grinders, electric drills, tape recorders, etc., use an electric motor as a rotating device that converts electrical energy to mechanical energy.The motor is a machine which converts the electric energy into mechanical energy.The generator is the device which converts mechanical energy into electrical energy. It is used to convert the mechanical power to electric power which varies in the magnitude with a specific frequency.

Image Motors are different from generators?

Image Motors Are Different from Generators?

Question 22:

What is the role of the two conducting stationary brushes in a simple electric motor?


The brushes are connected to the battery and touch the outerside of two halves of the split ring whose inner sides are insulatedand attached to the axle.

Question 23:

What is the difference between a direct current and an alternating current? How many times does AC used in India change directionin one second?


Direct current always flows in one direction but the alternatingcurrent reverses its direction periodically. The frequency of AC inIndia is and in each cycle it alters direction twice. ThereforeAC changes times in one second

Question 24:

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?


Fuse is used for protecting appliances due to short-circuiting oroverloading. The fuse is rated for a certain maximum current andblows off when a current more than the rated value flows throughit. If a fuse is replaced by one with larger ratings, the appliancesmay get damaged while the protecting fuse does not burn off. Thispractice of using fuse of improper rating should always be avoided.

Long Answer Questions

Question 25:

Why does a magnetic compass needle pointing North and South in the absence of a nearby magnet get deflected when a bar magnet or a current carrying loop is brought near it. Describe some salient features of magnetic lines of field concept.


Current carrying loops behave like bar magnets and both have theirassociated lines of field. This modifies the already existing earth’smagnetic field and a deflection results. Magnetic field has both directionand magnitude. Magnetic field lines emerge from N-pole and enter Spole. The magnetic field strength is represented diagrammatically by the degree of closeness of the field lines. Field lines cannot crosseach other as two values of net field at a single point cannot exist.Only one value, a unique net value, can exist. If in a givenregion, lines of field are shown to be parallel and equispaced, the field is understood to be uniform.

Image Magnetic field lines

Image Magnetic Field Lines

Question 26:

With the help of a labelled circuit diagram illustrate the pattern of field lines of the magnetic field around a current carrying straight long conducting wire. How is the right hand thumb rule useful to find direction of magnetic field associated with a current carrying conductor?


The magnetic field lines around a straight conductor (straight wire) carrying current are concentric circles whose centers lie on the wire.

Image Variable resistance

Image Variable Resistance

Right hand thumb rule states that if a current carrying straight conductor is supposedly held in the right hand with the thumb pointing towards the direction of current, then the fingers will wrap around the conductor in the direction of the field lines of the magnetic field.

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