## NCERT Textbook Solutions for class 10 science Chapter 13 Magnetic Effects And Electric Current

Q1. Which 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 centered on the wire.
Ans: (d) The field consists of concentric circles centered on the wire.

Q 2. The phenomenon of electromagnetic induction is
(a) the process of charging a body.
(b) the process of generating magnetic field due to a current passing through a coil.
(c) producing induced current in a coil due to relative motion between a magnet and the coil.
(d) the process of rotating a coil of an electric motor.
Ans: (c) producing induced current in a coil due to relative motion between a magnet and the coil.

Q 3. The device used for producing electric current is called a
(a) generator.
(b) galvanometer.
(c) ammeter.
(d) motor.
Ans: (a) generator.

Q 4. The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has permanent magnet.
(b) DC generator will generate a higher voltage.
(c) AC generator will generate a higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator.
Ans: (d) AC generator has slip rings while the DC generator has a commutator.

Q 5. At the time of short circuit, the current in the circuit
(a) reduces substantially.
(b) does not change.
(c) increases heavily.
(d) vary continuously.
Ans: (c) increases heavily.

Q 6. 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 of an electric supply.
Ans: (a) False, (b) True, (c) True, (d) False

Q 7. List three sources of magnetic fields.
Ans: (i)   Natural magnet
(ii)  Electro-magnet
(iii) Current carrying conductor

Other Chapters

## Class 10 Science Textbook Solutions

• Chapter 10 - Light: Reflection & Refraction
• Chapter 1 - Chemical Reactions & Equations
• Chapter 2 - Acids, Bases and Salts
• Chapter 3 - Metals and Non-metals
• Chapter 4 - Carbon and its Compounds
• Chapter 5 - Periodic Classification of Elements
• Chapter 6 - Life Processes
• Chapter 7 - Control and Coordination
• Chapter 8 - How do Organisms Reproduce
• Chapter 9 - Heredity and Evolution
• Chapter 11 - Human Eye and Colourful World
• Chapter 12 - Electricity
• Chapter 13 - Magnetic Effects of Electric Currents
• Chapter 14 - Sources of Energy
• Chapter 15 - Our Envioronment
• Chapter 16 - Management of Natural Resources

8. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current–carrying solenoid with the help of a bar magnet? Explain.
Ans: A solenoid behaves like a magnet (as a bar magnet) when current is flowing through the coil of solenoid. A solenoid consists of a coil of many circular turns of insulated copper wire and if current flows through a conducting wire a magnetic field is produced. Here, in solenoid a number of turns produces magnetic field resultant of which is same as magnetic field for a bar magnet.
The same poles of magnet repel each other and opposite poles attract. Now we keep a bar magnet’s North Pole towards one end of the solenoid, if it repels the solenoid end, we can conclude this end is North Pole of the solenoid and the other end is South Pole.

Q 9. When is the force experienced by a current–carrying conductor placed in a magnetic field largest?
Ans: When the direction of current flow is perpendicular to the direction of magnetic field, the force experienced by the current-carrying conductor is largest.
Reference:
Force experienced by moving charge Q with velocity v in magnetic field B is F = QvxB = QvBsin<v,B
So, F is largest when <v,B is 90 degree i.e. sin<v,B = 1
As the direction of charge flow and direction of current flow is opposite to each other, from the above equation we can say for largest value of F direction of current flow should be perpendicular to the direction of magnetic field.

Q 10. Imagine 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?
Ans: The direction of magnetic field is vertically downwards.

Q 11. Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?
Ans: Coming ...

Q 12. Name some devices in which electric motors are used.
Ans: Electric motors are used in electric fan, air-cooler, water-pump.

Q 13. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is
(i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?
Ans: (i) pointer of the galvanometer will deflect in one direction.
(ii) pointer of the galvanometer will deflect in opposite direction.
(iii) no deflection or no change in galvanometer pointer.

Q 14. Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.
Ans: Yes, if the current in the coil A is changed, some current will be induced in the coil B. Because, as current will be changed in coil A, the magnetic field around the coil will also be changed. As a result the coil B will face a changing magnetic field around it. We know changing magnetic field produces electric field (current). So a current will be induced in coil B.

Q 15. State the rule to determine the direction of a
(i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field.
Ans: (i) Right hand thumb rule.
(ii) Fleming’s left hand rule.
(iii) Fleming’s right hand rule.

Q 16. Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?
Ans: Coming ...

Q 17. When does an electric short circuit occur?
Ans: When the neutral wire and live wire come into direct contact, the current in the circuit increases highly and a short circuit occurs.

18. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Ans: Earth wire is connected to ground (earth surface) from an electronic device. When any extra leakage current is produced or somehow live wire become loose the earth wire pass the current to ground and make appliances and us safe from any unwanted accident.
For a metallic appliances if such leakage took place i.e. live wire become in contact with the metal body, earth wire safe human from electric shock.
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## NCERT textbook solutions for class 10 science Chapter 10 Light

Q1: Which one of the following cannot be used to make a lens?
(a)Water (b) Glass (c) Plastic (d) Clay.
Ans: Clay

Q2: The image formed by a concave mirror is observer to be virtual, erect and larger than the object. Where should be the position of the object?
Ans:  Object positing is in between the pole of the mirror and principal focus.

Q3: Where should an object be placed in front of a convex lens to get a real image of the size of the object?
Ans: At twice of the focal length i.e. at Center of curvature.

Q4: A spherical mirror and a thin spherical lens have each a focal length of -15cm. The mirror and the lens are likely to be – (a) both are concave (b) both are convex (c) the mirror is concave and the lens is convex (d) the mirror convex and the lens is convex
Ans: (a) both are concave

Q5: No matter how far you stand from a mirror, your image appears erect, the mirror is likely to be –
(a) Plane only (b) concave only (c) convex only (d) either plane or convex
Ans:  (d) either plane or convex

Q6: Which of the following lenses would you prefer to use while reading small letter found in a dictionary?
(a) a convex lens of focal length 50 cm (b) a concave lens of focal lens 50 cm (c) a convex lens of focal length 50 cm (d)  a concave lens of focal length 5 cm
Ans: (c) a convex lens of focal length 50 cm

Q7: We wish to obtain an erect image on an object using a concave mirror of 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image smaller or larger than the object? Draw a ray diagram to show the image formation in this case.
Ans: Object distance should be less than (focal length) 15 cm.
Image is virtual.
Image is larger than the object.

Q8: Name the type of the mirror used in the following situations –
(a) Headlights of the car, (b) side/rare view mirror of a vehicle, (c) solar furnace.
Ans:  (a) concave mirror, (b) convex mirror, (c) concave mirror

Other Chapters

## Class 10 Science Textbook Solutions

• Chapter 10 - Light: Reflection & Refraction
• Chapter 1 - Chemical Reactions & Equations
• Chapter 2 - Acids, Bases and Salts
• Chapter 3 - Metals and Non-metals
• Chapter 4 - Carbon and its Compounds
• Chapter 5 - Periodic Classification of Elements
• Chapter 6 - Life Processes
• Chapter 7 - Control and Coordination
• Chapter 8 - How do Organisms Reproduce
• Chapter 9 - Heredity and Evolution
• Chapter 11 - Human Eye and Colourful World
• Chapter 12 - Electricity
• Chapter 13 - Magnetic Effects of Electric Currents
• Chapter 14 - Sources of Energy
• Chapter 15 - Our Envioronment
• Chapter 16 - Management of Natural Resources

Q9. One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.
Ans: Yes this lens can produce a complete image of the object.

Experimental Varification: Consider in front of a convex lens a bulb s glowing(assuming light rays are coming parallel to the axis) and its image is formed at focus as a highly intense point.
Now if the lower half of the lens is covered with black paper, as shown, the image is still formed at the same position and of same nature but with a lesser intensity.
So, a complete image can be formed but intensity may vary.

Q10. An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.
Ans:
image is at 50/3 cm from the lens, image height is 3.3 cm, reduced, real(because magnification is negative), inverted

Q 11. A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.
Ans:
Q 12. An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.
Ans:
So, image is at 6 cm behind the mirror, virtual, erect and diminished.

Q 13. The magnification produced by a plane mirror is +1. What does this mean?
Ans: Magnification produced by a plane mirror is +1 means that: the image is the same size of the object and the image is virtual, erect.

Q 14. An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position of the image, its nature and size.
Ans:
Q 15. An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed, so that a sharply focused image can be obtained? Find the size and the nature of the image.
Ans:
Q 16. Find the focal length of a lens of power – 2.0 D. What type of lens is this?
Ans: Power of lens is P = -2.0 D
So, focal length, f = 1/P = 1/-2.0 = -0.5 m
Clearly focal lenght is -ve therefore, it is CONCAVE lens.

Q 17. A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
Ans: Doctor prescribe lens of power P = +1.5 D
So, focal length, f = 1/P = 1/1.5 = +1/1.5 m
Clearly focal lenght is +ve therefore, it is CONVEX lens.
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