A photocell is any of a wide range of sensors that react based on the presence of light or electromagnetic energy. They can be found in many different forms, from solar panels that use light to generate electricity, to photoresistors, which shift in resistance based on how much light is present.
Bond prices and yields are like a seesaw: when bond yields go up, prices go down, and when bond yields go down, prices go up. In other words, a move in the 10-year Treasury yield from 2.2% to 2.6% indicates negative market conditions, while a move from 2.6% to 2.2% indicates positive market performance.
If the bond later trades for $900, the current yield rises to 7.8% ($70 Ã· $900). The coupon rate, however, does not change, since it is a function of the annual payments and the face value, both of which are constant. Coupon rate or nominal yield = annual payments Ã· face value of the bond.