Unit and Measurement MCQ Questions & Answers in Basic Physics | Physics
Learn Unit and Measurement MCQ questions & answers in Basic Physics are available for students preparing for IIT-JEE, NEET, Engineering and Medical Entrance exam.
131.
In a vernier callipers $$N$$ divisions of vernier scale coincide with $$N - 1$$ divisions of main scale (in which length of one division is $$1\,mm$$ ). The least count of the instrument should be
133.
The current voltage relation of a diode is given by $$I = \left( {{e^{1000V/T}} - 1} \right)mA,$$ where the applied voltage $$V$$ is in volts and the temperature $$T$$ is in degree kelvin. If a student makes an error measuring $$ \pm 0.01\,V$$ while measuring the current of $$5\,mA$$ at $$300\,K,$$ what will b the error in the value of current in $$mA$$ ?
134.
Distance travelled by a particle at any instant $$'t'$$ can be represented as $$S = A\left( {t + B} \right) + C{t^2}.$$ The dimensions of $$B$$ are
A
$$\left[ {{M^0}{L^1}{T^{ - 1}}} \right]$$
B
$$\left[ {{M^0}{L^0}{T^1}} \right]$$
C
$$\left[ {{M^0}{L^{ - 1}}{T^{ - 2}}} \right]$$
D
$$\left[ {{M^0}{L^2}{T^{ - 2}}} \right]$$
Answer :
$$\left[ {{M^0}{L^0}{T^1}} \right]$$
In $$S = A\left( {t + B} \right) + C{t^2};B$$ is added to time $$t.$$
Therefore, dimensions of $$B$$ are those of time.
135.
Dimension of $$\frac{1}{{{\mu _0}{\varepsilon _0}}},$$ where symbols have their usual meaning, are-
A
$$\left[ {{L^{ - 1}}T} \right]$$
B
$$\left[ {{L^{ - 2}}{T^2}} \right]$$
C
$$\left[ {{L^2}{T^{ - 2}}} \right]$$
D
$$\left[ {L{T^{ - 1}}} \right]$$
Answer :
$$\left[ {{L^2}{T^{ - 2}}} \right]$$
we know that the velocity of light in vacuum is given by
$$\eqalign{
& c = \frac{1}{{\sqrt {{\mu _0}{\varepsilon _0}} }} \cr
& \therefore \frac{1}{{{\mu _0}{\varepsilon _0}}} = {c^2} = {L^2}{T^{ - 2}} \cr} $$
136.
In equation, $$r = {m^2}\sin \pi t,$$ where $$t$$ represents time. If the unit of $$m$$ is $$N,$$ then the unit of $$r$$ is
A
$$N$$
B
$${N^2}$$
C
$$Ns$$
D
$${N^2}s$$
Answer :
$${N^2}$$
Trigonometric ratio are a number and hence dimensionless.
137.
The pitch and the number of circular scale divisions in a screw gauge with least count $$0.02\,mm$$ are respectively
A
$$1\,mm$$ and 100
B
$$0.5\,mm$$ and 50
C
$$1\,mm$$ and 50
D
$$0.5\,mm$$ and 100
Answer :
$$0.5\,mm$$ and 100
Least count of a screw gauge $$ = \frac{{{\text{Pitch}}}}{{{\text{Number of circular scale divisions}}}}$$
$$\eqalign{
& = \frac{{1\,mm}}{{50}} \cr
& = 0.02\,mm \cr} $$
Therefore the pitch and no. of circular scale divisions are $$1\,mm$$ and 50 respectively.
138.
Which of the following statements is/are correct?
1. 345.726 has six significant figures.
2. 0.004289 has seven significant figures.
3. 125000 has three significant figures.
4. 9.0042 has five significant figures.
A
1 only
B
2 only
C
1, 3 and 4
D
2, 3 and 4
Answer :
1, 3 and 4
0.004289 has four significant figures.
139.
The period of oscillation of a simple pendulum is $$T = 2\pi \sqrt {\frac{L}{g}} .$$ Measured value of $$L$$ is $$20.0 \,cm$$ known to $$1 \,mm$$ accuracy and time for $$100$$ oscillations of the pendulum is found to be $$90s$$ using a wrist watch of $$1s$$ resolution. The accuracy in the determination of $$g$$ is-
140.
If $$x = at + b{t^2},$$ where $$x$$ is the distance travelled by the body in kilometer while $$t$$ is the time in second, then the unit of $$b$$ is
A
$$km/s$$
B
$$km - s$$
C
$$km/{s^2}$$
D
$$km - {s^2}$$
Answer :
$$km/{s^2}$$
As $$x = at + b{t^2}$$
According to the concept of dimensional analysis and principle of homogeneity
$$\eqalign{
& \therefore \,{\text{unit}}\,{\text{of}}\,x = {\text{unit}}\,{\text{of}}\,b{t^2} \cr
& \therefore \,{\text{unit}}\,{\text{of}}\,b = \frac{{{\text{unit}}\,{\text{of}}\,x}}{{{\text{unit}}\,{\text{of}}\,{t^2}}} = km/{s^2} \cr} $$