I heard quite a few of my friends saying the wavelength for the second harmonic wave is the same as the first one, but i seriously didn't understand the second question at all so i don't feel that bad actually, i'd have killed myself if that's a careless mistake. I think i've done my best in that practical, it's kind of hard, but i did everything that i knew, let's just keep our fingers crossed. Some students even say it's easier than Unit 3's practical, which i find unbelievable as u3 seemed way easier to me.