1

### AIPMT 2009

Maximum number of electrons in a subshell of an atom is determined by the following
A
2$l$ + 1
B
4$l$ $-$ 2
C
2n2
D
4$l$ + 2

## Explanation

Maximum number of electrons in a subshell = 2(2l+1) = 4l + 2
2

### AIPMT 2008

If uncertainty in position and momentum are equal, then uncertainty in velocity is
A
${1 \over m}\sqrt {{h \over \pi }}$
B
$\sqrt {{h \over \pi }}$
C
${1 \over {2m}}\sqrt {{h \over \pi }}$
D
$\sqrt {{h \over {2\pi }}}$

## Explanation

According to Heisenberg uncertainty principle

$\Delta p.\Delta x \ge {h \over {4\pi }}$ or m$\Delta v.\Delta x \ge {h \over {4\pi }}$

$\Rightarrow$ (m$\Delta v$)2 $\ge {h \over {4\pi }}$ ($\because$ $\Delta x$ = $\Delta p$)

$\Rightarrow$ $\Delta v \ge$ ${1 \over {2m}}\sqrt {{h \over \pi }}$
3

### AIPMT 2008

The measurement of the electron position is associated with an uncertainty in momentum, which is equal to 1 $\times$ 10$-$18 g cm s$-$1. The uncertainty in electron velocity is (mass of an electron is 9 $\times$ 10$-$28 g)
A
1 $\times$ 105 cm s$-$1
B
1 $\times$ 1011 cm s$-$1
C
1 $\times$ 109 cm s$-$1
D
1 $\times$ 106 cm s$-$1

## Explanation

$\Delta v$ = ${{1 \times {{10}^{ - 18}}} \over {9 \times {{10}^{ - 28}}}} = 1.1 \times {10^9}cm\,{s^{ - 1}}$
4

### AIPMT 2007

Consider the following sets of quantum numbers :

n l m s
(i) 3 0 0 +1/2
(ii) 2 2 1 +1/2
(iii) 4 3 -2 -1/2
(iv) 1 0 -1 -1/2
(v) 3 2 3 +1/2

Which of the following sets of quantum number is not possible ?
A
(i), (ii), (iii) and (iv)
B
(ii), (iv) and (v)
C
(i) and (iii)
D
(ii), (iii) and (iv)

## Explanation

(i) represents an electron in 3s orbital

(ii) is not possible as value of m varies from 0, 1, .... ($n$ -1)

(iii) represents an electron in 4f orbital

(iv) is not possible as value of m varies from -$l$ ... +$l$

(v) is not possible as value of m varies from -$l$ ... +$l$, it can never be grater than $l$