What is the distance for which ray optics is a good approximation for an aperture of 4 mm and wavelength 400 nm?

1. 40 m
2. 30 m
3. 20 m
4. 50 m

Two towers on top of two hills are 40 km apart. The line joining them passes 50 m above a hill halfway between the towers. What is the longest wavelength of radio waves, which can be sent between the towers without appreciable diffraction effects?

1. 11.23 cm
2. 12.5 cm
3. 10.02 cm
4. 13.87 cm

A parallel beam of light of wavelength \(500~\text{nm}\) falls on a narrow slit and the resulting diffraction pattern is observed on a screen \(1~\text m\) away. It is observed that the first minimum is at a distance of \(2.5~\text{mm}\) from the center of the screen. The width of the slit is:
1. \(0.43~\text{mm}\)
2. \(0.57~\text{mm}\)
3. \(0.13~\text{mm}\)
4. \(0.2~\text{mm}\)

In deriving the single slit diffraction pattern, at which angles the intensity is zero?
1. \(\dfrac{2 n \lambda}{a}\)

2. \(\dfrac{n \lambda}{a}\)

3. \(\dfrac{n \lambda}{2 a}\)

4. Zero