Download App

3. current electricity — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics3. current electricity1 Mark
MCQ
A cell sends a current through a resistance $R$ for time $t$. Now the same cell sends current through another resistance $r$ for the same time. If same amount of heat is developed in both the resistance, then the internal resistance of cell is
  • A
    $\frac{(R+r)}{2}$
  • B
    $\frac{(R-r)}{2}$
  • C
    $\frac{(R r)}{2}$
  • ✓
    $\sqrt{(R r)}$
✓

Answer

Correct option: D.
$\sqrt{(R r)}$
d
(d)

$H_1=\frac{E^2 R}{\left(R+r_1\right)^2}$

$H_2=\frac{E^2 R}{\left(r+r_1\right)^2}$

$\frac{R}{\left(R+r_1\right)^2}=\frac{r}{\left(r+r_1\right)^2}$

$\frac{r+r_1}{R+r_1}=\frac{\sqrt{r}}{\sqrt{R}}$

$\sqrt{R} r_1+r \sqrt{R}=\sqrt{r} r_1+R \sqrt{r}$

$r_1(\sqrt{R}-\sqrt{r})=\sqrt{R r}(\sqrt{R}-\sqrt{r})$

$r_1=\sqrt{R r}$

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 "M.C.Q (1 Marks)" from 3. current electricity→3. current electricity — all question types→Physics STD 12 Science question papers→CBSE Board STD 12 Science question papers→CBSE Board question paper generator→

Similar questions

An astronomical refracting telescope has an objective of focal length $20\,m$ and an eye piece of focal length $2\,cm$, then
→
Three particles having their charges in the ratio of $1 : 3 : 5$ produce the same spot on the screen in Thomson’s experiment. Their masses are in the ratio of
→
The net electric flux through a closed surface is:
→
The energy gap of silicon is $1.5\, eV$. At what wavelength the silicon will stop to absorb the photon....$Å$
→
According to classical physics, $10^{-15}\ m$ is distance of closest approach $(d_c)$ for fusion to occur between two protons. A more accurate and quantum approach says that ${d_c} = \frac{{{\lambda _p}}}{{\sqrt 2 }}$ where $'\lambda _p'$ is de-broglie's wavelength of proton when they were far apart. Using quantum approach, find equation of temperature at centre of star. [Given: $M_p$ is mass of proton, $k$ is boltzman constant]
→
In the given figure, battery E is balanced on 55 cm length of potentiometer wire but when a resistance of 10 W is connected in parallel with the battery then it balances on 50 cm length of the potentiometer wire then internal resistance r of the battery is
→
The angular resolution of a $10\,cm$ diameter telescope at a wavelength of $5000\,\mathop A\limits^o $ is of the order of
→
An ammeter of $100$ $\Omega$ resistance gives full deflection for the current of $10^{-5} \,amp$. Now the shunt resistance required to convert it into ammeter of $1\, amp$. range, will be
→
For equal point charges $Q$ each are placed in the $xy$ plane at $(0, 2), (4, 2), (4, -2)$ and $(0, -2)$. The work required to put a fifth change $Q$ at the origin of the coordinate system will be
→
A light ray enters a solid glass sphere of refractive index $\mu=\sqrt{3}$ at an angle of incidence $60^{\circ}$. The ray is both reflected and refracted at the farther surface of the sphere. The angle (in degrees) between the reflected and refracted rays at this surface is......
→