Which does not use a wheel and axle?
A doorknob,
a pencil sharpener,
a skateboard,
a rolling pin,
an eggbeater,
a saw.

Hydrogen atoms are excited by a laser to the =4n=4 state and then allowed to emit. what is the maximum number of distinct emission spectral lines (lines of different wavelengths) that can be observed from this system? 8 6 2 7 4 5 1 3 calculate the wavelength of the 4⟶14⟶1 transition. =λ=