Top 10, 10th Sci. Effects of electric current…🎷
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* How do we decide that a given the material a good conductor of electricity or is it an insulator?
Ans. A material having very low electrical resistance is called good conductor of electricity. Copper Cu, Gold Au, Silver Ag, Aluminium Al these are good conductors of electricity because free electrons are present in there last orbit.
Material having extremely high electrical resistance is called an insulator. Glass, wood, rubber, and plastic are electrically insulator because they do not have free electrons in their final orbitals.
* Heating effect of electric current
When a resistor is connected to an electric circuit, heat is produced in that resistor due to the current. This is known as the heating effect of the current.
Electric bulb, electric heater, electric cooker, fuse wire these instruments work on the heating effect of electric current.
* The unit of electric power is Watt ( W ).
1KW = 1000 W
* When 1 KWh kilo watt hour electric energy is used it is termed as 1 unit of energy.
* The Home electrical connection consists of ‘live’ ‘neutral’ and ‘Earth’ wires.
A. Live wire:- in actual electric current flows.
B. Neutral wire:- for completion of an electric circuit.
C. Earth wire:- is connected to the ground.
The potential difference between the ‘live’ and the ‘neutral’ wire is 220 volts (V).
* The function of fuse wire
As soon as high current flows in a circuit the fuse wire melts and breaks the circuit and any mishap/accident is avoided.
* MCB MINIATURE CIRCUIT BREAKERS
When the current in the circuit suddenly increases MCB this switch opens and current stops.
*Magnetic effect of electric current.
Electricity and magnetism are closely related. Hans Oersted played an important role in understanding ‘electromagnetism’. When a current passes through a metal wire the magnetic needle near the wire turns through a certain angle.
The unit of intensity of the magnetic field is turned as Oersted.
* Magnetic fields are produced around a conductor which carries electricity. As the distance from the wire increases the magnetic field reduces.
* Right hand thumb rule.
Imagine that we hold the conductor in our right hand in such a way that our thumb points in the direction of the current then the curled fingers show the direction of the magnetic line of force.
Solenoid
When a copper wire with a resistive coating is bound in a chain of loops then spring like structure is formed it is called solenoid.
The properties of the magnetic field produced by a bar magnet and the magnetic field of a solenoid are similar.
One of the open ends of a solenoid acts in the magnetic North pole (N)and the other as the magnetic South pole (S).
The magnetic lines of force inside the solenoid are parallel to each other.
The magnetic field in a solenoid is uniform.
* Flaming’s left hand rule
Stretch our left hand thumb, index finger and middle finger perpendicular to each other, if the index finger is in the direction of the magnetic field and the middle finger points in the direction of the current, then the direction of the thumb is the direction of force on the conductor.
* Electric motor
Definition:- Device which changes the electrical energy into mechanical energy is called electric motor.
* Faraday showed that an electric current can be produced in a conductor with the help of moving magnet.
* Galvanometer Voltmeter, Ammeter, electric motor all work on the same principle of Flaming’s left hand rule.
* Galvanometer
When small current flows through the coil of galvanometer the coil will rotate.
In galvanometer the pointer deflects on both the side of the zero mark depending on the direction of the current.
* Fleming’s right hand rule.
Stretch our thumb the index finger and middle finger in such a way that they will be perpendicular to each other. In this position the thumb indicates the direction of motion of the conductor the index finger the direction of the magnetic field and the middle finger shows the direction of induced current.
Fleming’s right hand rule is very useful, to show the direction of the industrial current.
* A surprise
Teenager Michael Faraday started working in a book binding shop. He got interested in science as he reads more books.
Sir Humphrey Davy appointed him as a laboratory assistant in the Royal Institute London. Though he was not formally educated, he discovered the laws of electromagnetic induction and the laws of electrolysis. Several Universities offered him honorary degrees but he politely refused to accept such honours.
* Alternating current (AC) and direct current (DC)
ALTERNATING CURRENT
Definition:- A current changing in magnitude and direction after equal intervals of time is called alternating current.
Alternating current is oscillatory.
AC can be transmitted over a long distance
* Direct current
The current which flows in only one direction is called DC.
DC is a non-oscillatory current.
DC cannot be transmitted over a long distance.
From the above point we can write the difference between alternating current and direct current.
In India the frequency of AC is 50 Hz.
Electric generator
Explain the construction and working of an electric generator. Draw a neat diagram and label it.
Definition:– A device that converts mechanical energy into electrical energy.
Construction
Copper wire coil ABCD kept between the two pieces of a strong horseshoe magnet. The two ends of the coil are connected to the conducting rings R1 and R2 via carbon brushes B1 and B2. Both the Rings fixed to the axle, but there is resistive coating in between the ring and the axle. B1 and B2 brushes are connected to a galvanometer.
Working:- the coil ABCD starts rotating when the axle is rotated with the help of a machine from outside. When the axle rotates branch AB goes up and the branch CD goes down.
According to Flaming’s right hand rule,electric current is produced in the branches AB and CD in the direction A —>B and C—> D. Thus, the current flows in the direction A —>B—>C—>D. After half rotation the branch AB takes the place of the branch CD and the branch CD takes the position of the branch AB. Therefore the induced current goes as D—>C—>B—>A. But, the branch A B is always in contact with brush B1 and the branch CD is in the contact with B2. Hence ,in the external circuit current flows from B1 to B2 i.e. opposite to the previous half rotation. This repeats after every half rotation so alternating current is produced.
The points are small but…. important.🥁
Column ‘A’ Column ‘B’
Electric current ampere
Electric resistance Ohm
Electric potential Volt
Work/energy Joule
Power Watt
The oham Resistance
Tungsten Bulb
Lead (Pb) and tin (Sn) Fuse
The oersted magnetic field
Electric energy – kilowatt-hour
voltmeter electric potential difference
Ammeter electric current
Nichrome Ni,Cr,Mn & Fe
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