With the laser, the diffracted images on the wall and the light source were on opposite sides of the grating. however, for the hydrogen and sodium lights, the light sources and the diffracted images were on the same side of the grating. do you see any contradiction?

The laser may have been shining a beam intense enough to show what the "light sources" - discharge tubes ? - couldn't show 'cos they were too weak, ie not enough photons flying around. 

34 degrees fahrenheit

Answer: 1.4 seconds which is the third optionexplanation: current is defined as the flow of charge per timetherefore, the equation that relates current, charge and time can be expressed as follows: i = δq / δtwhere: i is the current given = 1.8 ampereδq is the charge given = 2.5 coulombδt is the time required for the flow of the given charges to give the 1.8 ampere.substitute with the givens in the above equation to get the time as follows: 1.8 = 2.5 / δtδt = 2.5 / 1.8 = 1.38888 which is approximately 1.4 secondshope this was !