The photoelectric effect is observed when light irradiates a metal surface. Choose the correct

answers below. Only one answer per each part $($a$)-($e$).$

$($a$)$ Photoelectrons are emitted if:

the wavelength of light $$ is shorter than the threshold wavelength ${}_{th},$ that is $<msub\; id="EditorElement\_424772"><mrow><mi\; id="EditorElement\_424761"></mi></mrow><mrow\; id="EditorElement\_424771"><mi\; id="EditorElement\_424764">t</mi><mi\; id="EditorElement\_424766">h</mi><mtext\; id="EditorElement\_424768"></mtext></mrow></msub>$

the wavelength of light $$ exceeds the threshold wavelength ${}_{th},$ that is $>{}_{th}$

the light intensity I is below the threshold intensity $I_{th},$ that is $I{I}_{th}I>I_{th}$NINpropINprop$(I-I_{th})Nprop(I-h\frac{c}{{}_{th}})Nprop\frac{1}{\text{I}}$NNprop$Nprop{}^2$Nprop$\frac{1}{}I$

the light intensity I $is$ above the threshold intensity $I_{th},$ that $isI>I_{th}$

Electrons are emitted regardless $of$ the light wavelength and intensity.

$(b)$ Consider how the number $of$ electrons emitted per second, $N,$ depends $on$ the intensity $of$ light, I,

measured $in$ Watts. Assume the wavelength $is$ constant and the condition for electron emission $in$

part $(a)is$ satisfied. The number $of$ emitted electrons $is$:

proportional $to$ the light intensity: NpropI.

proportional $to$ the light intensity minus the threshold intensity: Nprop$(I-I_{th}).$

proportional $to$ the light intensity minus the threshold photon energy: Nprop$(I-h\frac{c}{{}_{th}}).$

inversely proportional $to$ the light intensity: Nprop$\frac{1}{\text{I}}.$

independent $of$ the light intensity.

$(c)$ Consider how the number $of$ emitted electrons, $N,$ depends $on$ the light wavelength. Assume that

the light intensity $is$ constant and the condition for electron emission $in$ part $(a)is$ satisfied. The

number $of$ emitted electrons $is$:

proportional $to$ the light wavelength: Nprop$.$

proportional $to$ the light wavelength squared: Nprop${}^2.$

inversely proportional $to$ the light wavelength: Nprop$\frac{1}{}.$