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Physics 2 Marks Questions

Model Paper 1 · Gujarat Board (GSEB) STD 12 Science (GSEB - English Medium). 12 questions.

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2 Marks Questions

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12 questions · self-marked practice — reveal the answer and mark yourself.

Question 12 Marks
Boron has two stable isotopes, ${ }_5^{10} B$ and ${ }_5^{11} B$. Their respective masses are $10.01294 u$ and $11.00931 u$ , and the atomic mass of boron is $10.811 u$ . Find the abundances of ${ }_3^{10} B$ and ${ }_3^{11} B$.
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Question 22 Marks
Work function of Zn is 3.74 eV . If the sphere of Zn is illuminated by the X rays of wavelength 12 Å, the maximum potential produced on the sphere is ..... $\left(h=6.625 \times 10^{-34} J s \right)$
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Question 52 Marks
Explain recombination coeflicient of intrinsic semiconductor and obtain the relation $n_t^2=n_{ c } n_{ h }$.
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Question 82 Marks
Discuss sign convention of distances for reflection by spherical mirror and refraction by spherical lens.
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Question 112 Marks
Write limitations of Ohm's law.
Answer
For certain materials and devices used in day to day life, voltage (V) and current (I) are not proportional to each other. So in such cases Ohm's law is not obeyed.
Image
(a) V and I are not proportional to each other.
In graph, dotted line part shows that Ohm's law is obeyed, where as continuous curve of the graph shows that Ohm's law is not obeyed.
$\rightarrow $ When current flows through conductor, Joule heat is produced. Hence, when conductor is heated, its resistance increases. Hence, for such materials V and I graph will be continuous curve.
Example : Diode, Transistor.
Image

(b) Relation between I and V depend on polarity of V . Hence, for same positive or negative values of voltage, different current values are obtained.
Example : PN junction diode.
$\rightarrow$ In graph shown for positive and negative value of voltage and current, scales are different.
Image
(c) I and V relation is not one-one function. For one value of current there are more than one values of voltage. For example, GaAs exhibit such behaviour.
$\rightarrow$ AV Figure shows $I \rightarrow V$ graph for GaAs. In such graph, $\frac{\Delta V }{\Delta I }$ is used to obtain resistance.
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Question 122 Marks
Write the law of conservation of charge. Give one example.
Answer
The total charge of the electrically isolated system is always conserved.
$\rightarrow$ When bodies are charged by rubbing, there is transfer of electrons from one bod to the other; no new charges are either created or destroyed.
$\rightarrow$ When we rub two bodies, what one body gains in charge the other body lose .
$\rightarrow $ Within an isolated system consisting of many charged bodies, due to interactions among the bodies, charges may get redistributed but remains conserved.
$\rightarrow $ It is not possible to create or destroy net charge carried by any isolated system, although the charge carrying particles may be created or destroyed in a process.
$\rightarrow $ When a neutron turns into a proton and an electron the proton and electron thus created have equal and opposite charges and the total charge is zero before and after the creation.
$\begin{array}{ll} 
& { }_0 n^1 \rightarrow{ }_1 p^1+-{ }_1 e^0 \\
\therefore & 0=+e+(-e)
\end{array}$
$\rightarrow$ Conservation of charge is a universal phenomena.
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