Coherence (physics) facts for kids

Coherence is a cool idea in physics that helps us understand how waves, like light waves, behave. Imagine waves marching along together!

In physics, two wave sources are called perfectly coherent if they always stay in step. This means they have a constant phase difference (they don't drift apart), the same frequency (they wiggle at the same speed), and the same waveform (they have the same shape). When waves are perfectly coherent, their peaks and troughs happen at the exact same time, and they have the same height.

Coherence is an ideal property of waves. It helps create steady interference patterns, which are patterns formed when waves combine.

The idea of coherence has a few different parts. These are like perfect examples that don't quite happen in real life. But they help us understand how waves work and have become a super important idea in quantum physics.

More generally, coherence describes how well different parts of a single wave, or several waves, are connected or "correlated" with each other.

What is Coherence?

Coherence is all about how organized and in-sync waves are. Think of it like a marching band: if everyone is marching in step, they are "coherent." If some people are out of step, they are less coherent. Waves that are coherent can combine in very specific ways, creating clear patterns.

Waves Working Together

For waves to be coherent, they need to meet a few conditions:

• Same Frequency: This means they wiggle or oscillate at the same speed. If one wave wiggles fast and another wiggles slowly, they can't stay in sync.
• Constant Phase Difference: This is about their starting point and how they stay aligned. If two waves start at the same point and keep that relationship as they travel, they have a constant phase difference. They don't drift apart.
• Same Waveform: This means they have the same shape. A smooth, regular wave can't be perfectly coherent with a bumpy, irregular one.

When waves meet these conditions, they can create amazing effects, like the bright and dark patterns you see in interference.

Why is Coherence Important?

Coherence is a big deal in many areas of physics and technology. It's what makes lasers work! A laser produces light waves that are highly coherent, meaning they are all marching perfectly in step. This is why laser beams are so focused and powerful.

Without coherence, many technologies wouldn't be possible. For example, in holography, which creates 3D images, coherent light is essential. It's also important in fields like fiber optics and telecommunications, where information is sent using light waves.

Coherence in Quantum Physics

In the tiny world of quantum physics, coherence is even more fundamental. It helps explain how tiny particles, like electrons, can also behave like waves. The idea of "quantum coherence" is key to understanding how future technologies like quantum computers might work. These computers rely on particles staying in a coherent state to perform calculations.

Images for kids

• 

  Figure 2: This shows a wave (red) whose phase changes over time, and a copy of the same wave (green) that's a bit delayed. When averaged over time, the interference disappears because they are sometimes in sync and sometimes out of sync.

• 

  Figure 3: Here, you see a wave packet (red) that changes its height over time, and a delayed copy (green). Since the wave packets don't overlap in time, there's no interference.

• 

  Figure 4: This graph shows how the brightness of light changes when waves interfere, depending on how much one wave is delayed. The blue line shows the actual brightness, and the black lines show the "envelope" or overall shape of the interference.

• 

  Figure 11: This image shows how light that isn't spectrally coherent (meaning it has many different colors or frequencies mixed up) can still look like continuous light, but with random changes in its phase and brightness.

See also

In Spanish: Luz coherente para niños