Which of the following Rays in large quantities has harmful effects on humans?

Options

A. IR-rays
B. Visible rays
C. Gamma rays
D. Ultra Violet Rays

Explanation

To determine which rays in large quantities have harmful effects on humans, we can analyze the provided options: infrared rays, visible rays, gamma rays, and ultraviolet rays.

### Step-by-Step Solution:

1. **Identify the Types of Rays**:
- The options given are infrared rays, visible rays, gamma rays, and ultraviolet rays. Each of these rays is a form of electromagnetic radiation with different properties and effects.

2. **Understand the Wavelengths**:
- **Infrared Rays**: Wavelengths range from about 700 nanometers to 1 millimeter. They are generally not harmful and are used in various applications like heating and remote controls.
- **Visible Rays**: Wavelengths range from about 400 nanometers (violet) to 700 nanometers (red). These rays are what we can see and are not harmful in normal exposure.
- **Gamma Rays**: Wavelengths are less than 10 picometers. They are very high energy and can be harmful, but they are not present in large quantities in everyday life.
- **Ultraviolet Rays (UV Rays)**: Wavelengths range from about 10 nanometers to 400 nanometers. They are present in sunlight and can cause harm to humans in large quantities.

3. **Assess the Harmful Effects**:
- **Infrared Rays**: Generally safe in normal exposure levels.
- **Visible Rays**: Not harmful; they are essential for vision.
- **Gamma Rays**: While they are harmful, they are not typically encountered in large quantities in daily life.
- **Ultraviolet Rays**: These rays can cause skin damage, sunburn, and increase the risk of skin cancer when exposure is excessive.

4. **Conclusion**:
- Among the options provided, **ultraviolet rays** are the rays that, when present in large quantities, have harmful effects on humans. They constitute about 10% of the total electromagnetic radiation output from the sun, which is significant enough to cause health issues.

### Final Answer:
**Ultraviolet rays** are the rays in large quantities that have harmful effects on humans.

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