Physics Vidyapith ✍️

What is Ammeter? An Ammeter is an instrument that is used to measure the electric current in the electric circuits directly in Ampere. The instrument which measures the current of the order of milliampere $(mA)$ is called the milliammeter. The internal resistance of the ideal ammeter is always zero. What is Galvanometer? The galvanometer is an instrument that is used to measure the very small amount of the electric charge passing through the circuit. The internal resistance of the Galvanometer is not zero. When a Galvanometer is used in the circuit and connected in the series to measure the electric current: The galvanometer is used in series to measure the electric current of the circuit so that the whole amount of the current passing through it. but the galvanometer will have some resistance due to the resultant resistance of the circuit increasing and the current in the circuit somewhat decreasing. Therefore the current read by the Galvanometer is less than the actua

The magnetic dipole moment of a revolving electron (Or Magnetic Moment due to Orbital Angular Momentum): An electron revolving in an orbit about the nucleus of an atom behaves like a current carrying loop. It is called a minute current-loop and produces a magnetic field. Every current loop is associated with a magnetic moment. Magnetic Dipole Moment of a Revolving Electron Let us consider, that the magnetic moment associated with a loop carrying current $i$ and having area $A$ is: $\mu_{L}= i.A \qquad(1)$ The current due to a revolving electron is $i=\frac{e}{T}$ Where $T$- The period of revolution of electron motion around the nucleus i.e $T=\frac{2 \pi r}{v}$ $e$- Charge on an electron So from the above equation $i=\frac{e}{\frac{2 \pi r}{v}}$ $i=\frac{ev}{2 \pi r} \qquad(2)$ The area of the current loop is: $A=\pi r^{2} \qquad(3)$ Now put the value of $i$ and $A$ in equation $(1)$ $\mu_{L}= \left( \frac{ev}{2 \pi r} \right) \l

Magnetic potential energy: When a current carrying loop is placed in an external magnetic field the torque is acted upon the current loop which tends to rotate the current loop in a magnetic field. Therefore the work is done to change the orientation of the current loop against the torque. This work is stored in the form of magnetic potential energy in the current loop. This is known as the magnetic potential energy of the current loop. Note: The current loop has magnetic potential energy depending upon its orientation in the magnetic field. Derivation of Potential energy of current-loop in a magnetic field: Let us consider, A current loop of magnetic moment $\overrightarrow{m}$ is held with its axis at an angle $\theta$ with the direction of a uniform magnetic field $\overrightarrow{B}$. The magnitude of the torque acting on the current loop or magnetic dipole is $\tau=m \: B \: sin\theta \qquad(1)$ Now, the current loop is rotated through an infinitesima

Current carrying Loop or Coil or Solenoid: The current carrying loop (or Coil or solenoid) behaves like a bar magnet. A bar magnet with the north and south poles at its ends is a magnetic dipole, so a current -loop is also a magnetic dipole. Equation of Magnetic Dipole Moment of Current carrying Loop: When a current loop is suspended in a magnetic field, it experiences the torque which tends to rotate the current loop to a position in which the axis of the loop is parallel to the field. So the magnitude of the torque acting on the current loop in the uniform magnetic field $\overrightarrow{B}$ is given by: $\tau=iAB sin\theta \qquad(1)$ Where $A$ - Area of the current loop We also know that when the electric dipole is placed in the electric field, it also experiences the torque which tends to rotate the electric dipole in the electric field. So the magnitude of the torque on the electric dipole in the uniform electric field $\overrightarrow{E}$ is given by: $\tau