What is Stopping Potential?

S7-SA4-0109

Grade Level:

Class 12

AI/ML, Physics, Biotechnology, FinTech, EVs, Space Technology, Climate Science, Blockchain, Medicine, Engineering, Law, Economics

Definition

What is it?

Stopping potential is the minimum negative voltage (potential difference) that needs to be applied to stop the most energetic photoelectrons from reaching the collector plate in a photoelectric effect experiment. It's the voltage required to make the photocurrent zero. This potential energy is equal to the maximum kinetic energy of the emitted photoelectrons.

Simple Example

Quick Example

Imagine you are trying to catch a cricket ball thrown by a friend. If your friend throws it very hard, you need to apply more force to stop it. Stopping potential is like the 'force' (voltage) you apply to stop the fastest-moving 'balls' (electrons) in an electrical circuit.

Worked Example

Step-by-Step

Let's say light of a certain frequency falls on a metal surface, and electrons are emitted. We want to find the stopping potential if the maximum kinetic energy of these emitted electrons is 3.2 x 10^-19 Joules. (Charge of an electron, e = 1.6 x 10^-19 Coulombs).

Step 1: Understand the relationship. The energy supplied by the stopping potential (eVs) must be equal to the maximum kinetic energy (KE_max) of the electrons.
---Step 2: Write down the formula: eVs = KE_max, where 'e' is the charge of an electron, and 'Vs' is the stopping potential.
---Step 3: Substitute the given values into the formula: (1.6 x 10^-19 C) * Vs = 3.2 x 10^-19 J.
---Step 4: Solve for Vs: Vs = (3.2 x 10^-19 J) / (1.6 x 10^-19 C).
---Step 5: Calculate the value: Vs = 2 Volts.
---Answer: The stopping potential is 2 Volts.

Why It Matters

Understanding stopping potential is crucial in fields like solar energy and sensor technology. It helps engineers design more efficient solar cells (EVs, Climate Science) and light detectors (Space Technology, Medicine). Scientists use this concept to study materials and develop new technologies in areas like quantum computing and medical imaging.

Common Mistakes

MISTAKE: Confusing stopping potential with threshold frequency. | CORRECTION: Stopping potential relates to the maximum kinetic energy of emitted electrons, while threshold frequency is the minimum frequency of light needed to emit any electron at all.

MISTAKE: Forgetting the negative sign for stopping potential in calculations or conceptual understanding. | CORRECTION: Stopping potential is a retarding potential, meaning it's applied in the opposite direction to stop the electrons. While the magnitude is positive, conceptually it's a negative voltage.

MISTAKE: Assuming stopping potential depends on the intensity of light. | CORRECTION: Stopping potential depends only on the frequency of light and the work function of the metal, not its intensity. Intensity affects the number of emitted electrons, not their maximum energy.

Practice Questions

Try It Yourself

QUESTION: If the maximum kinetic energy of photoelectrons emitted from a surface is 4.8 x 10^-19 J, what is the stopping potential? (Charge of electron = 1.6 x 10^-19 C) | ANSWER: 3 Volts

QUESTION: Light of frequency 'f1' produces photoelectrons with a maximum kinetic energy of 2 eV. If light of frequency 'f2' (where f2 > f1) is used, will the stopping potential be higher or lower? Explain. | ANSWER: Higher. Since f2 > f1, the electrons will have higher maximum kinetic energy, requiring a greater negative potential to stop them.

QUESTION: A metal has a work function of 2.5 eV. If light of energy 5.5 eV falls on it, what is the maximum kinetic energy of the emitted electrons, and what would be the stopping potential? (1 eV = 1.6 x 10^-19 J) | ANSWER: Maximum Kinetic Energy = 3 eV (5.5 eV - 2.5 eV). Stopping Potential = 3 Volts.

MCQ

Quick Quiz

Which of the following factors does the stopping potential primarily depend on?

Intensity of incident light

Frequency of incident light

Distance between anode and cathode

Area of the metal surface

The Correct Answer Is:

Stopping potential depends directly on the maximum kinetic energy of the emitted photoelectrons, which in turn depends on the frequency of the incident light and the work function of the metal. Intensity affects the number of electrons, not their maximum energy.

Real World Connection

In the Real World

In a solar panel (used widely in Indian homes and industries for green energy), sunlight hits a special material, releasing electrons. Stopping potential helps engineers understand the maximum energy these electrons can have. This knowledge is vital for designing efficient solar cells that convert more sunlight into electricity, powering everything from streetlights to homes in rural India.

Key Vocabulary

Key Terms

PHOTOELECTRIC EFFECT: The emission of electrons when light shines on a material | PHOTOCURRENT: The electric current produced by photoelectrons | KINETIC ENERGY: The energy an object possesses due to its motion | WORK FUNCTION: The minimum energy required to remove an electron from a solid | VOLTAGE: The electrical potential difference between two points

What's Next

What to Learn Next

Next, you should explore the 'Photoelectric Effect Equation' by Einstein. This equation directly links the energy of incident light, the work function, and the maximum kinetic energy of emitted electrons, helping you calculate stopping potential more deeply. Keep up the great work!