NEET Units and Measurements Previous year Question

1. (NEET 2020 Phase 1 )

The energy required to break one bond in DNA is 10^-20 J. This value in eV is nearly :

(A) 0.6

(B) 0.06

(C) 0.006

(D) 6

Correct answer is (B)

$1 e V = 1.6 \times 10^{- 19} J$

$1 J = \frac{1}{1.6 \times 10^{- 19}} e V$

$10^{- 20} J = \frac{10^{- 20}}{1.6 \times 10^{- 19}} e V$

= 0.06 eV

2. (AIPMT 2012 Prelims )

The damping force on an oscillator is directly proportional to the velocity. The units of the constant of proportionality are

(A) kg m s^{$-$ 1}

(B) kg m s^{$-$ 2}

(C) kg s^{$-$ 1}

(D) kg s

Correct answer is (C)

According to the question,

Damping force, F $\propto$ v

$\Rightarrow$ F = kv
where k is constant of proportionality.

$∴$ k = $\frac{F}{v}$ = $\frac{N}{m s^{- 1}}$ = $\frac{k g m s^{- 2}}{m s^{- 1}}$ = $k g s^{- 1}$

3. (AIPMT 2004 )

The unit of permittyvity of free space, $ε_{0}$ , is

(A) coulomb/newton-metre

(B) newton-metre²/coulomb²

(C) coulomb²/newton-metre²

(D) coulomb²/(newton-metre)²

Correct answer is (C)

F = $\frac{1}{4 π ε_{0}} \frac{q^{2}}{r^{2}}$

$\Rightarrow$ $ε_{0} = \frac{q^{2}}{4 π F r^{2}}$

$∴$ Unit of $ε_{0}$ = coulomb²/newton-metre²