CBSE Class 10 Answered
1. An electromagnet in its simplest form, is a wire that has been coiled into one or more loops, known as a solenoid.. When electric current flows through the wire, a magnetic field is generated. It is concentrated near (and especially inside) the coil, and its field lines are very similar to those for a magnet. The magnetic moment and the magnetic field of the electromagnet are proportional to the number of loops of wire, to the cross-section of each loop, and to the current passing through the wire.If the coil of wire is wrapped around a material with no special magnetic properties (e.g., cardboard), it will tend to generate a very weak field. However, if it is wrapped around a soft ferromagentic material, such as an iron nail, then the net field produced can result in a several hundred- to thousandfold increase of field strength.
2. If we have a long solenoid of length L, current I, and total number of turns N,
The magnetic field is essentially parallel to the axis of the solenoid, so B · ds is zero for the two vertical sides of the loop because the field is perpendicular to those sides.
The magnetic field outside the solenoid is considerably smaller than the filed inside, so we'll simply neglect that contribution to the integral. In the end the only side of the loop we'll count is the side inside the solenoid.If the solenoid has a uniform number of turns per unit length n = N/L, the current is nwI.
The factors of w cancel, giving B = mo nI
This is an almostuniform magnetic filed running parallel to the axis of the solenoid.
3. a hysteresis loop.
The "fatness" of the loop is a measure of the amount of energy wasted in changing the direction of magnetization (i.e., the hysteresis loss). Soft iron hysteresis loops are thin, because soft iron is easily magnetized, demagnetized, and remagnetized in the opposite direction. Steel loops, on the other hand, are fat because steel is far more reluctant to change its direction of magnetization.
4. The force is 0 when charges are at rest, when charges move in parallel or anti parallel to the magnetic filed, q = 0 deg. or 180 deg, F is 0 , force acts perpendicular to both B and V For charges of opposite sign the force acts in a direction opposite to that of positive charges.
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