Ok, I have few questions which I solved but the answers in he book do not match with the ones that I got.

Q1. The de-Brogile wavelength of a neutron at 927 degree C is {lambda}. What will be its wavelength at 27 degree C? I got 2 {lambda}, book says {lambda}/2

Q2. The distance between interatomic latice planes is 10A. What will be the maximum wavelength of X-Ray diffracted by the crystals? My ans 20A, book says 40A.

Q3. A parallel plate capacitor with plate area 'A' and separation 'd' is filled with dielectics k1 and k2 of equal thickness. What will its capacitance be? I have no idea about this one.

Q4. Two rain drops falling through air have radii in the ratio 2:3. What will be the ratio of their terminal velocity?