# Q. An electron jumps from the 4th orbit to 2nd orbit of hydrogen atom. Given the Rydberg's constant $R=10^5 cm^{-1}$ the frequency in hertz of the emitted radiation will be

AFMCAFMC 2010Atoms

Solution:

## Frequency, $v= \frac {c}{λ}=c.R \bigg (\frac {1}{n_1^2}- \frac {1}{n_2^2} \bigg )$ $\hspace15mm =3 \times 10^8 \times 10^7 \bigg (\frac {1}{2^2}- \frac {1}{4^2} \bigg )$ $\hspace15mm =\frac {9}{16} \times 10^{15} Hz$

You must select option to get answer and solution

## 1. The increase in pressure required to decrease the 200 L volume of a liquid by 0.004% (in kPa) is (Bulk modulus of the liquid ==2100 MPa)

Maharashtra CET 2006 Mechanical Properties Of Solids

## 2. To draw maximum current from a combination of cells, how should the cells be grouped?

AFMC 2006 Current Electricity

NEET 2019 Waves

## 4. The period of revolution of planet A around the sun is 8 times that of B. The distance of A from the sun is how many times greater than that of B from the sun?

AIPMT 1997 Gravitation

## 5. Two discs of same moment of inertia rotating about their regular axis passing through centre and perpendicular to the plane of disc with angular velocities $\omega_1$ and $\omega_2$ . They are brought into contact face to face coinciding the axis of rotation. The expression for loss of energy during this process is:-

NEET 2017 System Of Particles And Rotational Motion

## 6. The temperature of 100 g of water is to be raised from 24°C to 90°C by adding steam to it. The mass of the steam required for this purpose is

JIPMER 2015 Thermal Properties Of Matter

## 7. The diameter of a flywheel is increased by 1%. Increase in its moment of inertia about the central axis is

JIPMER 2015 System Of Particles And Rotational Motion

## 8. A body of mass 4 kg is accelerated upon by a constant force, travels a distance of 5 m in the first second and a distance of 2 m in the third second. The force acting on the body is

KCET 2008 Laws Of Motion

## 9. The spectrum of an oil flame is an example for ...........

KCET 2010 Dual Nature Of Radiation And Matter

## 10. The moment of inertia of a thin square plate ABCD, of uniform thickness about an axis passing through the centre O and perpendicular to the plane of the plate is where $I_1 , I_2, I _3$ and $I_4$ are respectively moments of inertia about axes 1, 2, 3 and 4 which are in the plane of the plate

IIT JEE 1992 System Of Particles And Rotational Motion