## UA practice problem frequency of light

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Linda Arroyo 3J
Posts: 15
Joined: Fri Apr 06, 2018 11:01 am

### UA practice problem frequency of light

6. The work function for lithium is 4.6 x 10−19 J.
a. What is the lowest frequency of light that will cause photoelectric emission?
The ANswer is 6.9 x 1014 Hz

I am just confused on what equation they used to solve this.

Xinyi Zeng 4C
Posts: 63
Joined: Fri Sep 28, 2018 12:18 am

### Re: UA practice problem frequency of light

First, consider E (photon)=hv, for frequency of light, v to be the lowest, E should be the lowest possible, too.
Now think about E(photon) - work function = E(excess) = Kinetic energy of the ejected electron
If we want E(photon) to be the lowest, we can take the E(excess) to be zero. Then, E (photon) = work function of Lithium.
Then, since we know E(photon), you can just use E=hv to solve for frequency.

Karina Jiayu Xu 4E
Posts: 58
Joined: Fri Sep 28, 2018 12:29 am

### Re: UA practice problem frequency of light

Can someone explain what a work function is? I think i got that wrong on the test because i thought a work function was work as a function of time.

Linh Vo 2J
Posts: 61
Joined: Sat Apr 28, 2018 3:00 am

### Re: UA practice problem frequency of light

Karina Jiayu Xu 4E wrote:Can someone explain what a work function is? I think i got that wrong on the test because i thought a work function was work as a function of time.

Yes I can. Work function is basically the idea of the energy required to eject or emit an electron. In the equation, E(photon) = work function + E(kinetic energy). Basically, the work function is the minimum amount of energy needed to eject an electron from a metallic surface (usually an ultraviolet wavelength). Work function is not work as a function of time. Work function can be denoted with a big O with a line striked through it.

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