How Frequency Affects the Maximum Kinetic Energy of Emitted Electrons

What happens to the maximum kinetic energy of emitted electrons when the frequency of the incident light decreases?

• A. It increases
• B. It remains the same
• C. It decreases
• D. It fluctuates

Answer: (C)

In the context of the photoelectric effect, the maximum kinetic energy of the emitted electrons is directly related to the frequency of the incident light. According to Einstein’s photoelectric equation, the maximum kinetic energy (K.E.) of the emitted electrons can be expressed as: K.E. = hf - φ where h is Planck’s constant, f is the frequency of the incident light, and φ is the work function of the material, which is the minimum energy needed to eject an electron from the surface. When the frequency of the incident light decreases, the energy of the photons (hf) decreases as well, since the energy is directly proportional to frequency. If the frequency falls below a certain threshold frequency (the point at which hf is equal to the work function φ), no electrons will be emitted, and thus the maximum kinetic energy will also reduce. If the frequency continues to decrease after this threshold, the energy of the photons becomes less than the work function, leading to a scenario where no electrons are emitted at all. As a result, the maximum kinetic energy of any emitted electrons decreases because the energy imparted to the electrons becomes insufficient to overcome the work function. Thus, it logically follows that as the frequency of the incident light decreases, the

When studying for your A Level Physics exam, it’s crucial to grasp the fundamentals of concepts like the photoelectric effect. Have you ever wondered what happens to the kinetic energy of emitted electrons when the frequency of incident light drops? You might have already guessed it — the maximum kinetic energy decreases. Let’s break this down.

Einstein’s photoelectric equation is pivotal here. It’s expressed as:

K.E. = hf - φ

In this equation, ( K.E. ) represents the maximum kinetic energy of emitted electrons, ( h ) is Planck's constant, ( f ) is the frequency of the incident light, and ( φ ) is the work function of the material — that is, the minimum energy an electron needs to escape the surface of a material.

Now, think of frequency as the heartbeat of light. The higher the frequency, the more energetic those photons are, letting electrons race away from their atoms. So, when the frequency decreases, what happens? That’s right — the energy of the photons also goes down. Since energy is directly tied to frequency, this means that fewer, less energetic photons are available to bump electrons loose.

Here’s the kicker: If the frequency plunges past a specific point, known as the threshold frequency, the energy (( hf )) dips below the work function (( φ )). Imagine it like a roller coaster that doesn’t have enough momentum to carry you over the peak; if the frequency doesn’t have enough energy to push the electron past the work function, it simply can’t escape. Thus, no electrons are emitted, and the maximum kinetic energy of any electrons that could’ve been emitted drops to nothing.

Now, considering these concepts, it’s essential to visualize the process. Picture photons colliding with a material like a pinball machine: when a fast pinball hits a target, it has enough energy to bounce off wildly. However, if that pinball slows down, it’s less likely to make things move.

But wait, there’s more! While we're grappling with these energy levels, think about how these principles apply in real-life technology. From photovoltaic cells harnessing solar energy to the intricate workings of cameras, the underlying mechanics of the photoelectric effect drive many modern innovations. So much hinges on the balance of light and energy, which demonstrates just how interconnected physics is with our everyday experiences.

Remembering these fundamental concepts — how frequency and kinetic energy relate, and how the work function transforms the otherwise energetic dance of electrons into a static wall — will serve you well on your journey through A Level Physics. So, next time you're tackling questions on the photoelectric effect, just think about that roller coaster analogy, and you might find a clearer path through the challenges of the exam!