1.

Calculate the strength of the transverse magnetic field required to bend all photoelectorns within a circle of radius 50 cm, when light of wavelength 4000Å is incident on a barium emitter. Work function of barium is 2.5eV. Given, `m_e=9.1xx10^(-31)kg, e=1.6xx10^(-19)C, h=6.6xx10^(-34)Js.`

Answer» Here, B=? , r=50cm=0.50m,
`lambda=4000Å=4000xx10^(-10)m=4xx10^-7m,`
`phi_02.5eV=2.5xx1.6xx10^(-19)J`.
As, `1/2mv_(max)^2=(hc)/lambda-phi_0`
or `v_(max)^2=2/m[(hc)/lambda-phi_0]`
`=2/(9.1xx10^(-31))`
`xx[((6.6xx10^(-34))xx(3xx10^8))/(4xx10^-7)-2.5xx1.6xx10^(-19)]`
`=20.88xx10^(10)`
`:. v_(max)=4.75xx10^5m//s`
Now, `Bev_(max)=mv_(max)^2//r`
or `B=(mv_(max))/(er)=((9.1xx10^(-31))xx(4.57xx10^5))/((1.6xx10^(-19))xx0.50)`
`5.2xx10^-6T`


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