Threshold wavelength of a photoelectric emission from a material is 600nm. Which of the following illuminating source will emit photoelectrons?

Options

A. 400W,, infrared lamp
B. 10W, ultraviolet lamp
C. 100W, ultraviolet lamp
D. Both B & C

Explanation

To determine which illuminating sources will emit photoelectrons from a material with a threshold wavelength of 600 nm, we can follow these steps:

### Step 1: Understand the concept of threshold wavelength
The threshold wavelength (λt) is the maximum wavelength of light that can cause photoelectric emission from a material. If the wavelength of the incident light is longer than the threshold wavelength, no photoelectrons will be emitted.

### Step 2: Identify the threshold wavelength
In this case, the threshold wavelength is given as 600 nm. This means that any light with a wavelength shorter than 600 nm can potentially cause photoelectric emission.

### Step 3: Analyze the options provided
We need to evaluate the wavelengths of the light emitted by the following sources:
1. **400W Infrared Lamp** - Infrared light typically has wavelengths longer than 700 nm, which is above the threshold wavelength of 600 nm. Therefore, it will not emit photoelectrons.
2. **10W Ultraviolet Lamp** - Ultraviolet (UV) light has wavelengths shorter than 400 nm. Since 400 nm is less than 600 nm, this source will emit photoelectrons.
3. **100W Ultraviolet Lamp** - Similar to the 10W UV lamp, this lamp also emits UV light with wavelengths shorter than 400 nm. Thus, it will also emit photoelectrons.
4. **Both B and C** - Since both the 10W and 100W UV lamps will emit photoelectrons, this option is correct.

### Step 4: Conclusion
The sources that will emit photoelectrons are the 10W Ultraviolet Lamp and the 100W Ultraviolet Lamp. Therefore, the correct answer is option 4: Both B and C.

### Summary of the solution:
- The threshold wavelength is 600 nm.
- Light with wavelengths shorter than 600 nm can cause photoelectric emission.
- The 10W and 100W UV lamps emit light with wavelengths shorter than 600 nm, thus they will emit photoelectrons.
- The 400W Infrared Lamp emits light with wavelengths longer than 600 nm, thus it will not emit photoelectrons.
- The correct answer is option 4: Both B and C.