Haryana State Board HBSE 10th Class Science Notes Chapter 13 Magnetic Effects of Electric Current Notes.
Haryana Board 10th Class Science Notes Chapter 13 Magnetic Effects of Electric Current
Magnetic Field and Magnetic Field Lines
Magnet and magnetism:
Substances that have property of attracting metals such as iron, nickel, cobalt, etc. are called magnets. This property of attraction possessed by magnets is called magnetism.
Bar magnet:
A magnet in the shape of a bar having two magnetic poles, nam&y the north pole and the south pole is known as a bar magnet.
Magnetic field:
The region surrounding the magnet in which magnetic force can be experienced is called magnetic field. Field lines are drawn to describe the extent of the magnetic peki.
Magnetic compass:
Magnetic compass is a small instrument which helps us to locate the -direction. The compass has a dial on which directions namely North N, South S, East E, and West W are marked.
Magnetic Field Due to a current-carrying conductor
Magnetic field formed due to a linear (straight) conductor carrying current:
It depends upon the following two factors —
- The magnetic field produced due to the current passing in the conductor is proportional to the electric current i.e. magnetic field intensity α electric current.
- The magnetic field intensity goes on decreasing as the distance from the conductor increases i.e. magnetic field intensity α 1/distance.
Right Hand Thumb Rule:
- The direction of magnetic field associated with the electric current can be found with the help of the ‘Right Hand Thumb Rule’.
- For knowing the direction of magnetic field, imagine that you are holding the conducting wire in your right hand so that your thumb points in the direction of the current (I), then the direction in which your fingers encircle the wire will give the direction of magnetic field around the wire.
Magnetic field produced due to a current carrying loop of wire:
The magnetic field B produced at the centre of the coil is —
- Directly proportional to the current (I) flowing through it i.e. B α I
- Inversely proportional to the radius (r) of the loop i.e. B α 1
- Directly proportional to the total number of turns N of the coil i.e. B α N. This means if a ring is made up of closely spaced N turns, the magnetic field at the centre of the ring will be N times stronger. Thus, magnetic field intensity
points in the direction of the current (I), then the direction in which your fingers encircle the wire will give the direction of magnetic field around the wire.
Magnetic field produced due to a current carrying loop of wire:
The magnetic field B produced at the centre of the coil is —
- Directly proportional to the current (I) flowing through it i.e. B α I
- Inversely proportional to the radius (r) of the loop i.e. B α 1/r
- Directly proportional to the total number of turns N of the coil i.e. B α N. This means if a the magnetic field at the centre of the ring will be N times stronger. Thus, magnetic field intensity
Solenoid:
- A long met wire turned several times to form the structure of a coiled cylinder is known as a solenoid.
- On passing electric current, a magnetic field is produced inside the solenoid. The magnetic field resulting due to N turns will be N times stronger than the magnetic Seki resulting by each circular coil.
The factors on which the strength of the magnetic field produced by a current carrying solenoid depends are —
- Number of turns (N) In the solenoid: More the number of turns (N) in the solenoid, stronger will be the magnetic field produced.
- Strength of the current (I): Greater the current (I) passing through solenoid, stronger will be the magnetic field produced.
- Nature of core material: If material such as a soft iron cylinder is used in making the solenoid core, the magnetic field will be quite strong.
Electromagnet:
A soft iron core placed inside a solenoid behaves like a powerful magnet when a current is passed through solenoid. Such a magnet (with magnetic field around) is called an electromagnet.
Force on a Current-Carn’in Conductor in a Magnetic Field
Fleming’s left hand rule:
Arrange your left hand such that the tore finger, the center finger and thumb remain at right angle to each other. Adjust your hand in such a way that the forefinger points in the direction of magnetic field and the centre finger points in the direction of current, then the direction in which the thumb points will be the direction of magnetic force.
Electric motor:
An electric motor is a rotating device which converts electric energy into mechanical energy.
Principie of electric motor:
- When a current carrying conductor (or a coil) is placed in a magnetic field, the conductor experiences force and it rotates.
- It is used in electric fan, mixer-grinder, washing machine, DVD players, etc.
Electromagnetic induction:
- When the magnetic line of force passing through a closed circuit change, voltage and hence a current is induced in It. This phenomenon is called electromagnetic induction. The voltage produced is called induced force (e.m.f.) and the current is called induced current.
- The direction of electric current can be found out with the help of Fleming’s right hand rule.
Fleming’s right hand rule:
Arrange the forefinger, middle finger and thumb of a right hand at right angle to one another. Adjust the forefinger in the direction of magnetic field, and thumb pointing in the direction of motion of conductor. The direction of middle finger will then indicate the direction of induced electric current.
Galvanometer:
A galvanometer is an instrument that can detect the presence of current in a circuit i.e. whether the current is flowing in the circuit or not.
Electric generator:
An electric generator is a device which converts mechanical energy into electric energy. The electric generator works on the principle of electromagnetic induction.
Types of electric current:
- DC current: The current that always flows in the same direction is known as direct current (DC). Batteries used in radio/cell phone, watch, laptop, etc. works on DC.
- AC current: The current that changes direction after equal intervals of time is known as alternating current (AC). Appliances such as fan, tubelight, TV, refrigerator. etc. run on AC Current.
Domestic Electric Circuits:
The current that comes to our house from the power stations is Alternate Current (AC). From power station, this power is transmitted to our houses through thick underground cables or over head electric poles and cables.
Three main wires enter the main board of our house. They are :
- Wire with red coloured insulation. This wire is known as live wire or positive.
- Wire with black coloured insulation. This wire is known as neutral wire or ‘negative’.
- Wire with green coloured insulation. This wire is known as earth (or earthing) wire.
Short circuit:
If positive (live) and negative wires touch each other accidently, such a situation is called short-circuit
Fuse:
A fuse is a safety device made out of small metallic strip with a low melting point. It works on the heating effect of the electric current.
Overloading:
If a large number of electrical appliances are switched on simultaneously, they start drawing large amount of current from the mains. When the current drawn exceeds the safety limit it is called over loading. Overloading may cause short- circuit. Fuse can help in preventing short-circuit.