Download App

MODEL PAPER 7 — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsMODEL PAPER 73 Marks
Question
Figure shows a rectangular conducting loop $\text{PQRS}$ in which arm $RS$ of length $I$ is movable. The loop is kept in a uniform magnetic field $B$ directed downward perpendicular to the plane of the loop. The arm $RS$ is moved with a uniform speed $v$.
Image

Deduce an expression for
$i$. the emf induced across the arm $RS$
$ii$. the external force required to move the arm and
$iii$. the power dissipated as heat.
✓

Answer

$i$. Let $RS$ moves with speed $v$ rightward and also $RS$ is at distances $x_1$ and $x_2$ from $PQ$ at instants $t_1$ and $t_2$, respectively.
Change in flux $, d \phi=\phi_2-\phi_1=B l\left(x_2-x_1\right)\left[\because \text { magnetic flux, } \phi=\vec{B} \cdot \vec{A}=B A \cos 0^0=B l x\right]$
$\Rightarrow d \phi=B l \ d x$
$ \Rightarrow \frac{d \phi}{d t}=B l \frac{d x}{d t}=B l v \quad\left[\because v=\frac{d x}{d t}\right]$
If resistance of loop is $R,$ then $I=\frac{v B I}{R}$
$ii$. Magnetic force $=B I I \sin 90^{\circ}$
$=\left(\frac{v B l}{R}\right) B l=\frac{v B^2 l^2}{R}$
Now, External force must be equal to magnetic force
$\therefore$ External force $=\frac{v B^2 l^2}{R}$
$\text { iii. As, } P=I^2 R=\left(\frac{ v B}{R}\right)^2 \times R=\frac{ v ^2 B^2 l^2}{R^2} \times R$
$\therefore P=\frac{ v ^2 B^2 l^2}{R}$

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 "3 Marks Question" from MODEL PAPER 7→MODEL PAPER 7 — all question types→Physics STD 12 Science question papers→Gujarat Board STD 12 Science question papers→Gujarat Board question paper generator→

Similar questions

  1. Using de Broglie's hypothesis, explain with the help of a suitable diagram, Bohr's second postulate of quantization of energy levels in a hydrogen atom.
  2. The ground state energy of hydrogen atom is - 13.6 eV. What are the kinetic and potential energies of the electron in this state?
→
The density of an ideal gas is $1.25 \times 10^{-3}gcm^3$ at STP. Calculate the molecular weight of the gas.
→
Two identical particles, each having a charge of $2.0 \times 10^{-4}C$ and mass of 10g, are kept at a separation of 10cm and then released. What would be the speeds of the particles when the separation becomes large?
→
What happens to the intensity of light from a bulb if the distance from the bulb is doubled? As a laser beam travels across the length of a room, its intensity essentially remains constant. What geomatrical characteristic of LASER beam is responsible for the constant intensity which is missing in the case of light from the bulb?
→
It is found experimentally that $13.6 eV$ energy is required to separate a hydrogen atom into a proton and an electron. Compute the orbital radius and the velocity of the electron in a hydrogen atom.
→
A metal sphere of radius R is charged to a potential V:
  1. Find the electrostatic energy stored in the electric field within a concentric sphere of radius 2R.
  2. Show that the electrostatic field energy stored outside the sphere of radius 2R equals that stored within it.
→
The following table gives the output of a two input logic gate.
  1. Identify the logic gate and draw its logic symbol.
  2. If the output of this gate is fed as input to a NOT gate, name the new logic gate so formed.
A
B
Y
0
0
1
1
0
1
0
1
1
1
1
0
→
Using Bohr’s postulates, obtain the expression for the total energy of the electron in the stationary states of the hydrogen atom. Hence draw the energy level diagram showing how the line spectra corresponding to Balmer series occur due to transition between energy levels.
→
Explain frequency and wavelength of electromagnetic spectrum.
→
Figure, shows a string stretched by a block going over a pulley. The string vibrates in its tenth harmonic in unison with a particular tuning fork. When a beaker containing water is brought under the block so that the block is completely dipped into the beaker, the string vibrates in its eleventh harmonic. Find the density of the material of the block.
→