class 10 magnetic effect of current NOTES

The region surrounding the magnet, in which the force of the magnet can be detected, is said to have a magnetic field.

Why does a compass needle get deflected?

Compass needle get deflected when brought near magnet due to the force of the magnet.
The lines along which the iron fillings align themselves represent magnetic lines of force.

Magnetic field is a quantity that has both magnitude and direction. The direction of the magnetic field is taken to be the direction in which a north pole of the compass needle moves inside it.

The field lines emerge from the north pole and merge at the south pole out side magnet.Inside the magnet, the direction of field lines is from its south pole to its north pole. Thus the magnetic field lines are closed curves. This is why no two field-lines are found to cross each other.

Magnetic field due to current carrying conductor

The direction of magnetic field produced by the electric current depends upon the direction of flow of current.If we reverse the direction of current then the direction of magnetic field produced by the electric current get changed.



The magnitude of the magnetic field produced at a given point increases as the current through the wire
increases.
The concentric circles representing the magnetic field around a current-carrying straight wire become
larger and larger as we move away from it.

Magnetic field due to current carrying circular loop: 

We know that the magnetic field produced by a current- carrying straight wire depends inversely on the distance.
We know that the magnetic field produced by a current- carrying conductor at a given point, depends directly on the current passing through it.
Therefore, if there is a circular coil having n turns, the field produced is n times as large as produced by a single turn. This is because the current in each circular turn has the same direction, and the field due to each turn then just adds up.

Magnet A substance which has the property of attracting other substances like iron filings and points in the north south direction when suspended freely is called a magnet.

Magnetic field The space around a magnet in which the force of attraction and repulsion due to it can be detected is called the magnetic field.

Magnetic field lines The curved paths along which the north pole of the compass needle moves in a magnetic field are called magnetic field lines. Magnetic field lines are used to represent a magnetic field.

Properties of magnetic field lines
The magnetic field lines never intersect each other because if they do so it means that at that point the compass needle would point towards two directions which is not possible.
They emerge at North Pole and merge at South Pole.
They are crowded near the poles and are far apart near the middle.
These are directed from North Pole to South Pole outside the magnet and from south to North Pole inside the magnet.

Compass needle A compass needle is a small bar magnet whose ends always point towards north south direction. The end pointing towards north is called North Pole and the end pointing towards south is called South Pole.

Magnetic field due to a current carrying straight wire The straight current carrying conductor produces a magnetic field around it in the form of concentric circular field lines with the conductor at the centre.

Factors affecting strength of magnetic field around a current carrying straight conductor. Strength of magnetic field is directly proportional to the current passing through the conductor and inversely proportional to the distance from the conductor. ( B a I and B a 1/r )

Right hand thumb rule or Maxwell’s clockwise rule    If we hold a straight wire in our right hand, and if the thumb represents the direction of current then the fingers represent the direction of magnetic field lines.

Magnetic field due to current carrying circular loop or coil         When the current is passed through circular loop or coil, the lines of force are circular near the wire but straight and parallel near the centre of loop or coil. Factors affecting magnetic field due to current carrying circular loop or coil.

Magnetic field due to current carrying circular loop at its centre is–
Directly proportional to the current passing through it.
Inversely proportional to the radius of loop.

Magnetic field due to current in a solenoid      The Magnetic field due to current carrying solenoid is similar to the magnetic field produced by a bar magnet. The ends of the solenoid act as North Pole and South Pole. The field lines inside the solenoid are in the form of straight parallel lines.

Factors affecting Magnetic field due to current in a solenoid

1. Magnetic field is directly proportional to the number of turns in the coil.

2. It is directly proportional to the current passing through it.

3. It is inversely proportional to the length of air gaps between the poles.

4. It depends on the nature of the core material used in the solenoid. Electromagnet.

An electromagnet consists of a long coil of insulated copper wire wrapped around a soft iron core. It is a temporary magnet as it works as long as current is passed through it. Factors affecting the strength of magnetic field of an electromagnet

The strength of magnetic field of an electromagnet is –

1. Directly proportional to the number of turns.

2. Directly proportional to the current flowing through it.

3. Inversely proportional to the length of air gaps between the poles.

Uses of electromagnet

1. They are used in electrical devices such as electric bell, electric fan, motor, and generator.

2. They are used for lifting and transporting large mass of iron.

3. They are used in medical practices for removing pieces of iron from wound and used in MRI.

Permanent magnets
A permanent magnet is made from steel alloys like carbon steel, chromium steel, cobalt steel, etc. They are weaker than electromagnets and their strength and polarity cannot be changed. Force on a current carrying conductor in a magnetic field.

A current carrying conductor placed in a magnetic field experi- ences a force due to the interaction between --- 

a. Magnetic field due to current carrying conductor and

b. External magnetic field in which conductor is placed.

Force on a current carrying conductor in a magnetic field

A current carrying conductor placed in a magnetic field experi- ences a force due to the interaction between
a. Magnetic field due to current carrying conductor and

b. External magnetic field in which conductor is placed.

Flemming’s Left Hand Rule 

If we stretch our thumb, fore finger and the middle finger of our left hand mutually perpendicular and if the fore finger represents the direction of magnetic field and the middle finger represents the direction of current then the thumb represents the direction of motion in conductor.
Electric motor 

A motor is the device which converts electrical energy into mechanical energy. It has a shaft which rotates continuously when current is passed through it. It is used in electric fans, mixer grinder, etc.

Principle of electric motor 

When a rectangular coil of copper wire is placed in a magnetic field and current is passed through it, a force acts on the coil which rotates it continuously. Electromagnetic induction. The production of electric current by moving a straight conductor in a magnetic field is called electromagnetic induction. It is the production of electricity from magnetism.

Flemming’s Right Hand Rule. 

If we stretch our thumb, fore finger and the middle finger of our right hand mutually perpendicular and if the fore finger represents the direction of magnetic field and the thumb represents the direction of motion in conductor then the middle finger represents the direction of induced current in the conductor.

Electric generator 

A generator is a machine which is used to generate electric current by converting mechanical energy into electrical energy. There are two types of generators – alternating current (AC) generator and direct current (DC) generator.

Principle of electric generator When a coil of copper wire is moved in a strong magnetic field, a current is induced in the coil.

Earthing 

The appliances that have metallic body (like electric iron, toaster, refrigerator, etc.) are connected with green wire which provides a low resistance conducting path for the current and keeps the body of appliance at the potential of the earth. This is called earthing. 

Earthing is done to save ourselves from electric shocks. 

Electric fuse 

The device having a short length of thin wire which is made of alloy lead and tin is called fuse wire or electric fuse. It has a very low melting point. It melts and breaks the circuit if the current exceeds the safe value. 

Fuse wire is connected in series in the circuit.


Overloading 

When too many electrical appliances of high power rating (electric oven, air conditioner, etc.) are switched on at the same time, a large current from the circuit is drawn. This is called overloading of the circuit. It may also occur when the live wire and the neutral wire come into direct contact.

Steps to avoid overloading

Short circuiting When the live wire and neutral wire come into direct contact, a large amount of current flows through the circuit due to very small resistance, this is called short circuiting. The heat produced during short circuiting is so high that it may cause fire.

CBSE 2014-15 Question

Magnetic needle placed at distance r from straight conductor of length 8r carrying current I shows a deflection of Ф degree.  what may be the deflection on passing the same current when conductor is bent in form of square and magnetic needle is placed at point of intersection of diagonals of square. Give reason to justify your answer.     See answer


Questions Bank Magnetic effects of electric current

solved questions -Magnetic effects of electric current

NCERT Magnetic Effects of Currents SOLVED QUESTIONS

NCERT Solution Magnetic Effects of Electric Current

CBSE- PHYSICS- IX- MOTION AND REST STUDY NOTES

A body is said to be in the state of rest when it remains in the same position with respect to time.
e.g.: The position of trees around the building is not changing with respect to the building. Then the trees are at rest.

A body is said to be in the state of motion, when it continuously changes its position with respect to time
e.g.: When we are cycling or running, we are changing position with respect to trees and buildings. we are said to be moving
DISTANCE AND DISPLACEMENT

Distance is the length of the path covered by a body. It has no sense of direction so it is a scalar quantity. Its SI unit of measurement is meter or m
The distance between the two places is not the same; it depends upon the path chosen.

Displacement:

The shortest distance, or distance travelled along a straight line, is known as displacement.If we draw a semicircle of radius 10cm. Then,
Displacement = r + r = 20cm
Distance = 2pr/2 = 10 x 22/7 cm = 31.4cm

UNIFORM MOTION AND NON UNIFORM MOTION

If an object covers equal distances in equal intervals of time, it is said to be in uniform motion.
If an object covers unequal distance in equal intervals of time, it is said to be in non-uniform motion.

MEASURING THE RATE OF MOTION

Speed :It is the distance travelled in one second (or) rate of distance travelled.

A car starts from Samastipur and reaches Patna in 6 hour. A bus takes 8 hour to travel the same distance. Which has moved faster? Why?

The car travels faster than the bus, because it covers the distance in a short time.

When a body covers a distance in a short time, it is said to be fast. If it takes more time to cover the distance, it is said to be slow.

Hence, Speed is the quantity used to say whether the motion is slow or fast.

Speed = Total Distance travelled/ Time taken
Speed has no sense of the direction of motion so it is a scalar quantity
SI Units: Speed is measured in m/s (or) m/s It can also be expressed in km/hour (or) kmh-1

Velocity : The speed with direction is known as velocity. So to measure the velocity, you should consider displacement instead of distance.Velocity is the displacement made in one second (or) rate of change of displacement. Rate of change means, change per second.

Velocity = Displacement/Time
It S. I.    Unit is also m/s

Uniform Velocity: Equal displacement covered by a body in equal intervals of time is known as uniform velocity.
Acceleration is the change in velocity of an object per second or rate of change of velocity.
Acceleration = Change in velocity/Time taken. The unit of acceleration is m/s2 or ms-2

There are two cases of of change of velocity
If the velocity of the body increases with time, the acceleration is positive, and the kind of motion is called accelerated motion.
If the velocity of the body decreases with time, the acceleration is negative (retardation), and the motion is called decelerated motion.

Uniform Acceleration: If an object travels in a straight line and its velocity increases or decreases by equal amount in equal intervals of time, then the acceleration of the object is uniform.

We can derive a formula for acceleration.
a= [v – u] / t

Where u - initial velocity, v - final velocity t – time

Distance - time graph

We can easily understand the relation between time and distance by using a graph.

Taking a suitable scale, a graph is drawn bytaking time along the x axis and distance along the y axis. The graph is known as distance – time graph.
In the graph for uniform speed is a straight line and curved for Non uniform speed.

CBSE PHYSICS: 10th SOURCES OF ENERGY Guess questions

SHORT QUESTIONS WITH ANSWERS (3 MARKS)

Q.1. How many groups of nuclei are generated in the fission of 235 U? what are their characteristics? Explain briefly the terms  (i) prompt (ii) delayed, and  (iii) spontaneous fission.

Ans.  Two groups of nuclei are generated in the fission of 235 U (i)One of these groups is a heavy group of nuclei with mass numbers ranging from 130 to 149,e.g., Barium and Lanthanum. (ii)The other groups are a lighter group of nuclei with mass numbers ranging from 85 to104, e.g., Krypton and Molybdenum. (iii)In prompt fission, the heavy nucleus disintegrates the moment it is bombarded. (iv)In delayed fission, a projectile (e.g., neutron) enters the target nucleus and causes an instability which results in the fission of the target nucleus after a short while. (v) Spontaneous fission is just out of the nature of the element.

Q.2. Write the four processes that can take place, after neutrons are emitted in a fission reaction. Which of these processes will cause the fission to continue? How is the energy of released neutrons lowered from 2 Me V to 0.025 Me V?

Ans. The four process that can take place after neutrons are emitted in a fission reaction are : ·         At least one such neutron hits another nucleus to cause its fission releasing more neutrons. ·         The neutrons may be captured by other nuclei without causing their fission. ·         The neutrons may be captured by other nuclei (present either in the fissionable material or in               the  surrounding container without causing fission. ·         The neutrons may not interact with other nuclei and may escape the system. ·         The energy of released neutrons is lowered from 2Me V to0.025Me V by passing them             through a moderator.

Q.3. (i) write the value of solar constant of sun.   (ii) what type of mirror is used in Box Type Solar cooker?   (iii) why it is difficult to use hydrogen as a source of energy?  (iv)what is the maximum temperature attained in a concave reflector type solar cooker?   (v)Fossil fuels are classified as non-renewable source of energy. Explain why.

Ans. (i) 1.4kW/m2 (ii) Plane mirror.  (iii) It cannot be stored safely as (i) it burns with explosion and (ii) has low ignition temperature. (iv) about 200oC.  (v)fossil fuels cannot be replenished. It takes millions of years for their formation.

Q.4. (a) Why is solar cooker box covered with a plane glass plate?  (b) Why is the energy of water flowing in a river considered to be an indirect form of solar energy? (c) Write one advantage of nuclear fission reaction.

Ans. (a) the plane glass plate traps heat radiation and thus produces a kind of greenhouse effect. Consequently, the temperature inside the cooker become high (100oC to140oC). (b) Solar energy changes into potential energy of water vapour rising in the atmosphere during evaporation of water from rivers, seas, oceans and other water masses. The water vapour from clouds and also cover mountains with snow. When the clouds bring rain and the snow on the mountains melts, their potential energy changes into kinetic energy of water flowing in the rivers and streams. (c) Amount of energy produced in nuclear fission is enormous, one kg of U-235, on fission produces as much energy as 2500 tons of coal produces on combustion.

Q.5. (a) State  one limitation of solar energy available from solar cells.   (b) What is the minimum wind velocity required to obtain useful energy with a wind will  ? (c) Define the term ‘nuclear fission’.

Ans. (a) the electricity (dc) produced by solar cells panels is stored by charging dc batteries which can be used only to operate dc devices. To operate any ac device, this dc has to be first converted into ac by using inverters. (b) 15km/h (c) Nuclear fission- In Nuclear fission, the heavy nucleus distingerates, the Moment it is bombarded with law energy neutrons, it splits up into two Righer nuclei and tremendous amount of energy is released. Extra score Guess questions

Q.1. Name two gases, other than carbon-dioxide that are given out during burning of fossil fuels and contribute towards acid rain formation?

Ans. Sulphur dioxide and Nitric oxide.

Q.2. Why are many thermal power plants set up near coal or oil fields?

Ans. Coal or petroleum is used to heat water to generate steam required for running for turbines in thermal power plants. Thus, if thermal power plants are set up near coal or oil fields, the cost of transportation of coal or petroleum is greatly reduced.

Q.3. Justify in one sentence that hydropower (hydel electricity) is a renewable source of energy.

Ans. Hydropower is generated from water flowing out of the dam which gets filled up again when it rains (or the snow melts) through the rivers which supply water to the dam.

Q.4. Out of two solar cookers, one was covered by a plane glass slab and the other was left open. Which of the two solar cookers will be more efficient and why?

Ans. The solar cooker covered by plane glass slab will be more efficient than the one which is left open. This is due to the reason that the plane glass slab enables the cooker to trap heat inside it. On this account, the temperature inside the cooker rises. In fact, the plane glass slab placed on the cooker produces a kind of greenhouse effect.

Q.5. A student constructed a box type solar cooker. He found that it did not work efficiently. What could this be due to? Give any four possible mistakes in the construction and operation of the cooker. What maximum temperature can ordinarily be reached inside a solar cooker?

Ans.  The four possible mistakes in the construction and operation of the cooker are: ·         The interior of solar cooker might not have been blackened, ·         Plastic cover might have been used instead of glass cover, ·         The cooker might not have been properly insulated, ·         The cooker utensils might not have been blackened.

Q.6. A student has set up a solar cooker in a box by using a black painted aluminum sheet, a black cooking vessel, some glass wool, a glass sheet and a mirror plate. What is the role of each item used in the solar cooker?

Ans. (i) Black painted aluminum sheet absorbs heat radiation (ii) Glass wool, which is a bad conductor of heat, prevents the loss of heat. (iii) Glass sheet traps the heat radiation in the box. (iv)Mirror plate reflects the heat radiation onto the glass sheet.

Q.7. Solar energy can be harnessed directly as well as indirectly. Give two examples of each type.

Ans. Solar energy is used directly as heat or by converting it directly into electricity. Examples: solar cooker (or solar water heater) and solar cell panels. Solar energy is used indirectly by converting it into chemical energy (like biomass energy), harnessing the energy of wind, sea waves, tides and ocean thermal energy. Example: Biogas plants and windmills.

Q.8. What is anaerobic degradation?

Ans. Anaerobic degradation is the process of decomposition of animal and plants wastes by anaerobic bacteria in the presence of water but in the absence of air to form methane (the main constituent of biogas), carbon dioxide, hydrogen and hydrogen sulphide. Anaerobic bacteria (or anaerobe) is a minute organism that can live without free oxygen.

Q.9. what is a solar power plant? Name one such plant in our Country.

Ans. Sunlight is concentrated on black painted pipes (filled with water) with the help of concave reflectors. Due to solar heat, water starts boiling and then changes into steam. The steam so produced rotates a steam turbine which drives a generator to produce electricity. A solar thermal power plant of 22k W capacity is in operation at Solajipally village in Andhra Pradesh. A 50kW solar thermal power plant is being installed at the Twal Pahari Premises of the Solar Energy Centre, Gurgaon (Haryana).

Q.10. How can wood be made a renewable source of energy ?

Ans. Wood can be made a renewable source of energy only if trees are planted in a planned manner.

Q.11. What causes the wind to blow?

Ans. Equatorial regions on the Earth receive more solar radiation than other parts of the Earth. As such, the air at equatorial regions is hotter and rises upwards into the atmosphere. The cooler air from other regions (especially polar regions) starts blowing to the equatorial regions to fill the space vacated by hot air. It is this moving air which is called wind.

Q.12.To which category of fuel does hydrogen belongs to?

Ans. Hydrogen ,which is available in plenty in water on earth, is classified as a renewable sources of energy.

Q.13. Why is Nuclear fuel classified as renewable source of energy?

Ans. Nuclear fuel is required only in a very small quantity to generate electric power and as such is inexhaustible.

Q.14. Why the Geothermal energy is classified as a renewable sources of energy?

Ans. Geothermal energy will be available for a long time.

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