MCQ
The photoelectric threshold wavelength for potassium (work function being $2eV$) is ........... $nm$
- A$310 $
- ✓$620 $
- C$1200 $
- D$2100 $
✓
Answer
Correct option: B.
$620 $
b
(b) $\lambda = \frac{{12375}}{{{W_0}}} = \frac{{12375}}{2} = 6187.5{Å}$$ = 620\;nm$
(b) $\lambda = \frac{{12375}}{{{W_0}}} = \frac{{12375}}{2} = 6187.5{Å}$$ = 620\;nm$
Need a full question paper?
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.
Explore more
Similar questions
A star producing light of wavelength $6000 Å$ moves away from the earth with a speed of $5\, km/sec$. Due to Doppler effect the shift in wavelength will be......$\mathop A\limits^o $ $(c = 3 \times {10^8}m/\sec )$
→Energy required for the electron excitation in $Li^{++}$ from the first to the third Bohr orbit is.....$eV$
→A heater $A$ gives out $300\, W$ of heat when connected to a $200\, V$ $d.c.$ supply. Asecond heater $B$ gives out $600\, W$ when connected to a $200\,v$ $d.c$. supply. If a series combination of the two heaters is connected to a $200\, V$ $d.c$. supply the heat output will be ................. $W$
→A radioactive sample decays by $\beta$ -emission. In first two seconds $‘n’$ $\beta$ -particles are emitted and in next $2\ seconds$ , $‘0.25n’$ $\beta$ -particles are emitted. The half life of radioactive nuclei is ...... $sec$
→A wire of length $1 \,m$ is moving at a speed of $2\,ms^{-1}$ perpendicular to its length and a homogeneous magnetic field of $0.5\,T$. The ends of the wire are joined to a circuit of resistance $6$ $\Omega$ The rate at which work is being done to keep the wire moving at constant speed is
→A ball rolls without slipping. The radius of gyration of the ball about an axis passing through its centre of mass $K$. If radius of the ball be $R$, then the fraction of total energy associated with its rotational energy will be
→A man standing on a road hold his umbrella at $30^° $ with the vertical to keep the rain away. He throws the umbrella and starts running at $10\, km/hr$. He finds that raindrops are hitting his head vertically, the speed of raindrops with respect to the road will be......... $km/hr$
→A motor having an armature of resistance $2\Omega $ is designed to operate at $220 \,V$ mains. At full speed, it develops a back $e.m.f$. of $210\,V$. When the motor is running at full speed, the current in the armature is......$A$
→When a pressure of $100$ atmosphere is applied on a spherical ball, then its volume reduces to $0.01\%$. The bulk modulus of the material of the rubber in $dyne/c{m^2}$ is
→Assertion : Charges are given to plates of two plane parallel plate capacitors $C_1$ and $C_2$ (such that $C_2 = 2C_1$ ) as shown in figure. Then the key $K$ is pressed to complete the circuit. Finally the net charge on upper plate and net charge the circuit. Finally the net charge on upper plate and net charge on lower plate of capacitor $C_1$ is positive.
→Reason : In a parallel plate capacitor both plates always carry equal and opposite charge.