List of top Physics Questions on Modern Physics

Which of the following statements is correct during the formation of a PN junction?

What is the minimum wavelength in the Lyman series of the hydrogen spectrum?

The measured length of a rod is (20.0 $\pm$ 0.2) cm. The percentage error in the measurement is:

A radioactive substance has a half-life of 5 days. If its initial mass is 80 g, the mass remaining after 15 days is:

The resistance of a semiconductor decreases when its temperature increases because:

A diode is forward biased by 0.7 V. If the forward resistance is 10 $\Omega$, the current through the diode is:

Photons of energy \(4\,\text{eV}\) are incident on a metal surface whose work function is \(2\,\text{eV}\). If the intensity of this incident light is doubled, the maximum kinetic energy of the emitted photoelectrons will:

The work function of Mg, Cu, Ag, Li are \(3.7, 4.8, 4.3, 2.5\,\text{eV}\) respectively. A wavelength of \(300\,\text{nm}\) light is shined on them. The metals which undergo photoelectric effect are

Light of wavelength \(1000\AA\) incidents on a metal surface of work function \(6\,eV\). The maximum kinetic energy of photoelectrons is

तीन संख्याएं: (प्रोटॉनों की संख्या, न्यूट्रॉनों की संख्या, त्रिज्या) एक नाभिक की पहचान बताती हैं। \((1, 0, r_1)\) और \((4, 4, r_2)\) से निरूपित दो नाभिकों के लिये \(\frac{r_1}{r_2}\) का मान क्या होगा?

प्रकाश विद्युत प्रभाव के किसी प्रायोगिक अध्ययन में कार्य फलन \(\phi_0\) वाले एक धातु का प्रयोग किया जा रहा है। आपतित फोटॉन का वह लघुतम तरंगदैर्ध्य क्या होगा जिससे कि द्रव्यमान \(m\) वाले उत्सर्जित इलेक्ट्रॉन का दे ब्रॉग्ली तरंगदैर्ध्य, आपतित फोटॉन के दे ब्रॉग्ली तरंगदैर्ध्य के समान हो जाए? [\(h\) प्लांक का स्थिरांक है, \(c\) प्रकाश का वेग है और \(\phi_0 \ll mc^2\)]

एक समतल सतह पर अभिलम्बतः आपतित, संचरित क्षमता \(P\) वाले, फोटॉनों के एकवर्णी किरण पुंज का विचार करें। इस आपतित पुंज का 10% भाग अवशोषित हो जाता है, 10% भाग पारगमित हो जाता है और शेष भाग सतह के द्वारा परावर्तित हो जाता है। यदि प्रकाश का वेग \(c\) हो तो इस सतह पर पुंज के द्वारा कितना बल लग रहा है?

The three numbers: (number of protons, number of neutrons, the radius) characterize a nucleus. What is the value of $\frac{r_1}{r_2}$ for two nuclei characterized by $(1, 0, r_1)$ and $(4, 4, r_2)$?

An experimental study of the photoelectric effect involves a metal of work function $\phi_0$. What is the smallest wavelength of the incident photon to photoemit an electron of mass $m$ which has the same de Broglie wavelength as that of the incident photon? [Given $h$ is the Planck's constant, $c$ is the speed of light, and $\phi_0 \ll mc^2$]

Two identical photo cathodes receive light of frequencies \( f_1 \) and \( f_2 \). If the velocity of photo electrons (of mass m) coming out are respectively \( V_1 \) & \( V_2 \) then:

Sodium and Copper have work functions 2.3 eV and 4.5 eV respectively. Then the ratio of their threshold wavelengths is nearly:

Two identical parallel metal plates A and B, having fine holes at their centers are connected to a power supply as shown in the figure. An electron having energy 200 eV is directed to pass through these holes from A to B. The de Broglie wavelength of the electron when it comes out of plate B is:

Work function of a metallic surface is 5.01 eV. When a light of wavelength 2000Å falls on the metallic surface, it emits photo electrons. The potential difference required to stop the fastest photo electron is? (in Volt)

The de Broglie wavelength of a particle of mass $m$ moving with a velocity $v$ is given by

The work function of a metal depends on

According to the Special Theory of Relativity, what happens to the length of an object as its velocity approaches the speed of light?

The energy of photon is given by: ____.

A screw gauge has a pitch of 0.1 mm and 100 divisions on its circular scale. When its both jaws touch, the fifth division of its circular scale coincides with zero. When a sphere is placed between the jaws, the reading of the linear scale is 5 mm and the 50th division of the circular scale coincides with zero of the main scale. Find the diameter of the sphere.

A rod of length L is heated from temperature \( T_1 \) to \( T_2 \). Let \( T_2 - T_1 = \Delta T \) and the expansion of the rod be \( \Delta L_1 \). The rod is further heated from \( T_2 \) to \( T_3 \) such that \( T_1 + T_3 = 2T_2 \). Find the expansion of the rod \( \Delta L_2 \):

Electron and proton are accelerated with the same potential to achieve de-Broglie wavelengths of \( \lambda_1 \) and \( \lambda_2 \). Given \( m_p = 1849 \, m_e \), find the ratio \( \lambda_1/\lambda_2 \):