Q. A charge $q$ at a distance $x$ from straight current carrying wire is moving towards it with speed $v$, experiences a magnetic force of magnitude $F$. If the distance of the charge from the wire is $2 x$ (all other conditions remaining the same) then the force would be

KCETKCET 2022 Report Error

A

$F$

B

$2 F$

C

$\frac{F}{2}$

D

$\frac{F}{4}$

Solution:

Magnetic force, $F=q v B, $
$\therefore F \propto B$
Magnetic field at a point distant ' $x$ ' due to a straight conductor carrying current is
$F=\frac{\mu_{0}}{4 \pi} \frac{2 I }{ x } $
$ \therefore F \propto \frac{1}{x}$
$\therefore B \propto \frac{1}{ x }$

Questions from KCET 2022

1. A truck of mass $0.5$ Ton is moving with a speed of $6\, ms ^{-1}$. Sand is poured at the rate of $10\, Kg$ per minute. How much force is needed to keep it moving with the same speed?

2. A horizontal force $F$ is applied on a block of weight $W$ to hold against a vertical wall. The minimum value of force needed to hold the block if the coefficient of friction of the surface is $\mu$

3. A bird is inside a wire cage hung from a spring balance. The spring balance reading is $R_{1}$ when the bird is flying and $R_{2}$ when it is at rest inside the cage. Which of the following is correct?

4. 6. An ideal heat engine gives out heat at $77^{\circ} C$ to have a $30 \%$ of efficiency. The temperature of the source is

5. In an auditorium absorption co‐efficient of an open window is

Physics Most Viewed Questions

1. If $E$ and $G$ respectively denote energy and gravitational constant, then $\frac{ E }{ G }$ has the dimensions of:

NEET 2021 Physical World, Units and Measurements

2. The de Broglie wavelength of an electron moving with kinetic energy of $144 \,eV$ is nearly

NEET 2020 Dual Nature of Radiation and Matter

3. A car starts from rest and accelerates at $5\, m / s ^{2}$ At $t=4\, s$, a ball is dropped out of a window by a person sitting in the car. What is the velocity and acceleration of the ball at $t =6\, s$ ? (Take $\left. g =10\, m / s ^{2}\right)$

NEET 2021 Motion in a Straight Line

4. A wheel with $20$ metallic spokes each $1\, m$ long is rotated with a speed of $120\, rpm$ in a plane perpendicular to a magnetic field of $0.4\, G$. The induced emf between the axle and rim of the wheel will be, $(1 G = 10^{-4}\, T)$

NEET 2020 Electromagnetic Induction

5. A barometer is constructed using a liquid (density $= 760 \,kg/m^{3})$ What would be the height of the liquid column, when a mercury barometer reads $76\, cm$ ?
(density of mercury $= 13600 kg/m^{3})$

NEET 2020 Mechanical Properties of Fluids