A laser of wavelength 1524.8 nm is split using a beamsplitter into two similar power beams. Using mirrors, the beams are aligned to approximately co-propagate with the same polarisation and they cross each other with a small angle of 23.66 degrees. In the crossing region transverse to the beams there is an optical standing wave (optical lattice) - what is the distance between successive bright (or dark) intensity zones in μm? [Cross-polarised beams have no standing wave. 0.3% Accuracy needed.]

(2) (a) you have a simple circuit that consists of only a battery (δvbat=1.5v) and two resistors with resistance r1=10ω and r2=5ω, connected in series with each other. what is the current running through the battery? (b) you re-arrange your circuit so now r2 is attached in parallel to r1 rather than in series. what is the current running through the battery? (c) you add an additional resistor r3=7ω on the same branch as r2. what is the current running through the battery? (d) what is the power dissipated in r3?