Explain with a neat labelled diagram how the magnetic forces on a… - Vidyadip

Question

Explain with a neat labelled diagram how the magnetic forces on a current loop produce rotary motion as in an electric motor.

✓

Answer

Consider a current-carrying rectangular loop $A B C D$, within a uniform magnetic field $\frac{mg}{a B}$, from below figure. Lead wires and commutator are not shown for simplicity. The coil is free to rotate about a fixed axis. Suppose the sides $A B$ and $C D$ are perpendicular to the field direction.

The magnetic force on each segment act at the centre of mass of that segment. The direction of the force on each segment can be found using the right hand rule for the cross product or from Fleming’s left hand rule.
The magnetic forces on the short sides AD and CB are, in general, equal in magnitude, opposite in direction and have the same line of action along the rotation axis. Hence, these forces cancel out and does not produce any torque. The magnetic forces on the long sides AB and CD are also equal in magnitude and opposite in direction but their lines of action are different. Hence, these forces constitute a couple and tend to rotate the coil about the central axis.
A commutator (not shown) reverses the direction of the current through the loop every half-revolution so that the torque always acts in the same direction.

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "Answer the following in Detail" from Magnetic Fields due to Electric Current→Magnetic Fields due to Electric Current — all question types→Physics STD 12 Science question papers→Maharashtra Board STD 12 Science question papers→Maharashtra Board question paper generator→

Similar questions

It is observed in an experiment on photoelectric effect that an increase in the intensity of the incident radiation does not change the maximum kinetic energy of the electrons. Where does the extra energy of the incident radiation go? Is it lost? State your answer with explanatory reasoning.

Derive the ideal gas equation, $\mathrm{PV}=\mathrm{nRT}$.
OR
Derive the equation of state for an ideal gas.

Three capacitors of capacities $8 \mu F , 8 \mu F$ and $4 \mu F$ are connected in series and a potential difference of $120 V$ is maintained across the combination. Calculate the charge on the capacitor of capacity $4 \mu F$. Also calculate the potential difference across it.

A stretched sonometer wire emits a fundamental note of frequency $256 Hz$. Keeping the stretching force constant and reducing the length of the wire by $10 cm$, the frequency becomes $320 Hz$. Calculate the original length of the wire.

State and explain the hydrostatic paradox. OR Explain hydrostatic paradox.

Using Ampere's law, obtain an expression for the magnetic induction near a current-carrying straight infinitely long wire.

Explain the phenomenon of polarization of light by reflection.

Describe the construction of the cyclotron with a neat labelled diagram

State the uses of a potentiometer.

An electron in an atom is revolving round the nucleus in a circular orbit of radius $5.3 \times 10^{-11} m$, with a speed of $2 \times$ $10^6 ms^{-1}$ Find the resultant orbital magnetic moment and angular momentum of electron. (charge on electron $e =$ $1.6 \times 10^{-19} C$, mass of electron $m _{ e }=9.1 \times 10^{-31} kg$.)