Tag: physics

Questions Related to physics

The total energy of an electron in the ground state of hydrogen atom is $-13.6\space eV$. The potential energy of an electron in the ground state of $Li^{2+}$ ion will be

physics nuclei gamma decay change in nucleus due to radioactive decay alpha, beta and gamma particles (rays) and their properties

  1. $122.4\space eV$

  2. $-122.4\space eV$

  3. $244.8\space eV$

  4. $-244.8\space eV$

Show answer
Correct Option: D
Explanation:

Therefore, for ${ Li }^{ 2+ }$ ion, Total energy is $- 13.6\times 9 = 122.4\ eV$
But, $-K.E= T.E= \dfrac { P.E }{ 2 } $
Therefore, $P.E$ is $-244.8\ eV$

The ground state energy of Hydrogen atom is $–13.6eV$. The potential energy of the electron in this state is:

physics nuclei gamma decay change in nucleus due to radioactive decay alpha, beta and gamma particles (rays) and their properties

  1. $0eV$

  2. $-27.2eV$

  3. $1eV$

  4. $2eV$

Show answer
Correct Option: B
Explanation:

The ground state energy of hydrogen atom $=13.6eV$

Potential energy $=2$ energy of electron
                             $=2(-13.6\ eV)$
                             $=-27.2\ eV$

In which of the following systems will the radius of the first orbit (n = 1) be minimum ?

physics nuclei gamma decay change in nucleus due to radioactive decay alpha, beta and gamma particles (rays) and their properties

  1. hydrogen atom

  2. deuterium atom

  3. singly ionized helium

  4. doubly ionized lithium.

Show answer
Correct Option: D
Explanation:

Radius of the first orbit of an atom  $R _1 = \dfrac{0.529}{Z}$  $A^o$
$\implies \ R _1 \propto\dfrac{1}{Z}$
where $Z$ is the atomic number of Hydrogen-like atom.
Since $Z$ is maximum for doubly ionized lithium, thus radius of first orbit is minimum in doubly ionized lithium.

Joule's effect is due to:

physics effects of electric current joule's law of heating thermal effect of electric current heating effect of electric current

  1. Collision of electrons

  2. Collision of free electrons with positive ions

  3. Collision of positive ions

  4. All

Show answer
Correct Option: B
Explanation:

Joule's effect is due to collision of free electrons with positive ions.

A/c to Joules's law, if the potential difference across a conductor having a material of specific resistance (P) remains constant, then the heat produced in the conductor is directly proportional to

physics effects of electric current joule's law of heating thermal effect of electric current heating effect of electric current

  1. $\displaystyle P$

  2. $\displaystyle { P }^{ 2 }$

  3. $\displaystyle \frac { 1 }{ \sqrt { P } } $

  4. $\displaystyle \frac { 1 }{ P } $

Show answer
Correct Option: D
Explanation:

Let the specific resistance of the material be  $P$.

$\therefore$  Resistance of the conductor        $R = \dfrac{P L}{A}$
According to Joule's heating effect,  heat produced     $H = \dfrac{V^2t}{R}$

$\therefore$   $H = \dfrac{V^2 t}{PL/A}  = \dfrac{V^2A t}{L}\dfrac{1}{P}$              $\implies H\propto \dfrac{1}{P}$

Joule's heating effect is

physics effects of electric current joule's law of heating thermal effect of electric current heating effect of electric current

  1. Reversible

  2. Irreversible

  3. Both

  4. None

Show answer
Correct Option: B
Explanation:

Joule heating effect is irreversible that means if the direction of current in a resistor is reversed, the cooling of resistor does not occur whereas heating of the resistor takes place.

Heat produced via Joule's heating effect    $H = i^2Rt$ 

From Joule's Law of heating, the heat produced, $H =$

physics effects of electric current joule's law of heating thermal effect of electric current heating effect of electric current

  1. $\dfrac{{I}^{2}}{Rt}$

  2. $\dfrac{{I}^{2}R}{t}$

  3. $\dfrac{{R}^{2}I}{t}$

  4. ${I}^{2}Rt$

Show answer
Correct Option: D
Explanation:

Work done (heat produced) $= {I}^{2}Rt  \   Joule$


$I=$ current, $R =$ Resistance

$t =$ time in seconds

J (Joule's mechanical equivalent of heat) is equal to

physics effects of electric current joule's law of heating thermal effect of electric current heating effect of electric current

  1. 2400J

  2. $\displaystyle 4.18J{ cal }^{ -1 }$

  3. $\displaystyle 2.2J{ cal }^{ -1 }$

  4. 1000J

Show answer
Correct Option: B
Explanation:
According to Joule's law, mechanical equivalent of heat    $J = \dfrac{W}{Q}$
Mathematically    $J = 4.18$  $Jcal^{-1}$ if work done and heat produced is measured in joules and calories respectively.

From below which one is the equation for Joule's law of heating effect of electricity?

physics effects of electric current joule's law of heating thermal effect of electric current heating effect of electric current

  1. $H=I^2Rt$

  2. $H=IR^2t$

  3. $H=IRt^2$

  4. $H=\dfrac{It^2}{R}$

Show answer
Correct Option: A
Explanation:

According to Joule's law of heating,  heat produced in a resistor     $H = I^2Rt$

where $I$ and $t$ are the current flowing through the resistor and time of current flowing respectively.

If a current $i$ flows steadily through a resistor $R$ for a time $t$. Then total heat energy supplied to the resistor is given by:

physics effects of electric current joule's law of heating thermal effect of electric current heating effect of electric current

  1. $\dfrac{R}{it}$

  2. $iR^{2}t^{2}$

  3. $i^{2}Rt$

  4. $V^{2}it$

Show answer
Correct Option: C
Explanation:

According to Joule's law of heating, total heat energy supplied to the resistor, $H=i^{2}Rt$