What is Photon Energy? | Simple Explanation for Class 10

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What is the Energy of a Photon (Basic)?

Grade Level:

Class 10

AI/ML, Physics, Biotechnology, Space Technology, Chemistry, Engineering, Medicine

Definition

What is it?

The energy of a photon is the amount of energy carried by a single 'packet' of light. This energy depends on the light's frequency or wavelength; higher frequency light like blue light has more energy per photon than lower frequency light like red light.

Simple Example

Quick Example

Imagine you are buying mobile data. A 1GB pack for Rs. 100 has a certain 'amount' of data. Similarly, a photon carries a specific 'amount' of energy. Just like a 2GB pack might cost more than a 1GB pack, a photon of blue light carries more energy than a photon of red light.

Worked Example

Step-by-Step

Let's calculate the energy of a photon if its frequency is 5 x 10^14 Hz.

Step 1: Understand the formula. The energy of a photon (E) is calculated using the formula E = hf, where 'h' is Planck's constant (6.626 x 10^-34 J.s) and 'f' is the frequency of the light.

---Step 2: Identify the given values. Frequency (f) = 5 x 10^14 Hz. Planck's constant (h) = 6.626 x 10^-34 J.s.

---Step 3: Substitute the values into the formula. E = (6.626 x 10^-34 J.s) * (5 x 10^14 Hz).

---Step 4: Multiply the numerical parts. 6.626 * 5 = 33.13.

---Step 5: Multiply the exponential parts. 10^-34 * 10^14 = 10^(-34+14) = 10^-20.

---Step 6: Combine the results. E = 33.13 x 10^-20 J.

---Step 7: Convert to standard scientific notation (optional but good practice). E = 3.313 x 10^-19 J.

---Step 8: State the answer. The energy of the photon is 3.313 x 10^-19 Joules.

Why It Matters

Understanding photon energy is crucial for developing technologies like solar panels (converting light to electricity) and medical imaging (like X-rays). It helps engineers design better cameras, allows scientists to study stars, and guides doctors in using light for treatments, opening doors to careers in renewable energy, space technology, and medicine.

Common Mistakes

MISTAKE: Confusing frequency with wavelength directly in the formula E=hf. | CORRECTION: Remember E=hf uses frequency (f). If you are given wavelength (lambda), you first need to convert it to frequency using the speed of light (c = f * lambda) before using E=hf.

MISTAKE: Forgetting the units or using incorrect units for Planck's constant or frequency. | CORRECTION: Always use SI units: Joules for energy, Hertz (Hz) for frequency, and Joules-seconds (J.s) for Planck's constant.

MISTAKE: Incorrectly handling powers of 10 during multiplication or division. | CORRECTION: When multiplying powers of 10, add the exponents. When dividing, subtract them. For example, 10^-34 * 10^14 = 10^(-34+14) = 10^-20.

Practice Questions

Try It Yourself

QUESTION: A photon has a frequency of 3 x 10^14 Hz. Calculate its energy. (Planck's constant h = 6.626 x 10^-34 J.s) | ANSWER: E = hf = (6.626 x 10^-34 J.s) * (3 x 10^14 Hz) = 1.9878 x 10^-19 J

QUESTION: If a photon has an energy of 4.0 x 10^-19 J, what is its frequency? (h = 6.626 x 10^-34 J.s) | ANSWER: f = E/h = (4.0 x 10^-19 J) / (6.626 x 10^-34 J.s) = 6.037 x 10^14 Hz

QUESTION: A green light photon has a wavelength of 500 nm (nanometers). Calculate its energy. (Speed of light c = 3 x 10^8 m/s, h = 6.626 x 10^-34 J.s) | ANSWER: First, convert wavelength to meters: 500 nm = 500 x 10^-9 m = 5 x 10^-7 m. Then, calculate frequency: f = c / lambda = (3 x 10^8 m/s) / (5 x 10^-7 m) = 0.6 x 10^15 Hz = 6 x 10^14 Hz. Finally, calculate energy: E = hf = (6.626 x 10^-34 J.s) * (6 x 10^14 Hz) = 3.9756 x 10^-19 J

MCQ

Quick Quiz

Which of the following colors of visible light has photons with the highest energy?

Red

Yellow

Green

Violet

The Correct Answer Is:

Violet light has the highest frequency and shortest wavelength among visible light colors. Since photon energy is directly proportional to frequency (E = hf), violet light photons carry the most energy.

Real World Connection

In the Real World

You see the energy of photons in action every day with your smartphone camera! When you take a photo, tiny light sensors capture photons. Each photon carries energy that helps create the image. Also, the LED lights in your home emit photons, and their specific energy determines the color of the light you see, whether it's a warm yellow or a cool white.

Key Vocabulary

Key Terms

PHOTON: A tiny packet or quantum of light energy | FREQUENCY: The number of waves passing a point per second, measured in Hertz (Hz) | WAVELENGTH: The distance between two consecutive crests or troughs of a wave | PLANCK'S CONSTANT: A fundamental physical constant (h) that relates the energy of a photon to its frequency

What's Next

What to Learn Next

Great job understanding photon energy! Next, you can explore the 'Photoelectric Effect,' which explains how this photon energy can actually knock electrons out of a metal surface, a concept vital for solar cells and other modern technologies. It builds directly on what you've learned here.