Class X Science Important notes of Chapter 12- Magnetic effect of electric current-Second part
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Q1. What is a solenoid? Show the magnetic field through a solenoid.
Ans. The solenoid is a winding of wire in the shape of a cylinder, it works just like a bar magnet one of its end connected with the negative terminal of the battery become north pole and other end connected with the positive terminal become a south pole of the solenoid. The direction of the magnetic field is followed by the right-hand thumb rule, If the direction of current in it is from right to left then the direction of the field is anticlockwise and if the direction of current is from left to right then field direction is clockwise. The magnetic field around a solenoid is shown bellow. The strength of the magnetic field around it is proportional to the amount of current flowing in it and the number of turns in the coil.
Q2. State Flaming’s left-hand rule.
Ans. If three fingers, middle finger, thumb and four fingers of the left hand are to be stretched perpendicular to one another in such a way that the middle finger shows the direction of the current, four-finger shows the direction of the magnetic field then thumb will show the direction of magnetic force.
Q3. State Flaming’s right-hand rule.
Ans. The right-hand fingers thumb, four-finger, and middle finger are to be stretched 90° to one another in such a way that four-finger shows the direction of the magnetic field, thumb shows the direction of motion of the conductor then middle finger will show the direction of induced current in the conductor.
Q4.What is electromagnetic induction?
Ans. When a conductor moves in a magnetic field or magnetic field around it varies a voltage is produced across the ends of the conductor known as electromagnetic induction and the kind of current passed through it is known as induced current.
As an example, if in a coil we insert a magnet directing its north pole into the coil then the indicator of galvanometer deflected left side, it is because of a voltage produced across the conductor due to the change in the magnetic field.
When we enter the magnet directing its south pole inside it then the indicator of the galvanometer deflects the right-hand side, it is because of the direction of current changes across the coil.
Q5.Draw a label diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?
The basic principle of an electrical motor is based on the property of magnets that opposite poles attract each other and similar poles repel.
In the first figure, a couple of magnetic force between N-S and S – N tends to rotate the suspended magnet at the middle of a showcase magnet. On the same case, a coil between two poles N and S of two different magnets also arranged to be rotated .
Principle- The electric motor is based on the principle of electromagnetic, the rule is, if a charge moves or current is flowing through a conductor in a magnetic field then a magnetic force is exerted on the charge or conductor. The direction of the force on the conductor is given by the right-hand rule of Flaming which is already discussed in question number (3).
Working- When motor is switched on , the current moves from D to A perpendicular to the direction of the magnetic field from left to right then a downward force is applied on AD which tends to move AD in the downward direction and when current moves B to C an upward force is applied on BC which tend to move BC in the upward direction, a couple of forces in AC and BC rotate the coil between N and S pole of both magnet.
Role of the split ring– The split rings are connected to the brushes which are used to pass current from the circuit to the armature(coil) , the split ring changes the direction of electric current and maintains the direction of current in one way only that’s why these split rings are known commutator (means communicator) . It works like this after half rotation position of AD is replaced by BC and the direction of current reversed, the split rings S and P also change their positions in place of each other but brushes E and F remains on their position, so the split ring S come in contact of the brush E and the direction of current is maintained in a unidirectional way or in other words the current flows in the same direction as before and armature of the motor carried to rotate in the same direction.
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