Grating Order Three-Row Scan - Wave Optics: Interference and Diffraction Step by Step

Order raises the required sine marker until the toy sine limit rejects the row. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

First order closes at two fifths

Spacing 5 m times sine marker 2/5 gives 2 m. Order 1 times wavelength 2 m gives 2 m, so this row is accepted.

5\ \text{m}\cdot\frac{2}{5}=2\ \text{m}\quad m\lambda=1\cdot2\ \text{m}=2\ \text{m}\quad A=1

Second order needs four fifths

Spacing 5 m times sine marker 4/5 gives 4 m. Order 2 times wavelength 2 m gives 4 m, so this row is accepted.

5\ \text{m}\cdot\frac{4}{5}=4\ \text{m}\quad m\lambda=2\cdot2\ \text{m}=4\ \text{m}\quad A=1

Third order cannot fit inside the sine limit

Spacing 5 m times sine marker 1 gives 5 m. Order 3 times wavelength 2 m gives 6 m, so this row is rejected.

5\ \text{m}\cdot1=5\ \text{m}\quad m\lambda=3\cdot2\ \text{m}=6\ \text{m}\quad A=0