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.
Yield to Put is the annual yield on a bond, assuming it will be put (that is, sold back to the issuer) on the first permissible date after purchase. Bonds are quoted in this manner only. Note: if they sell at a price below the Put price. Therefore, the yield includes both interest and price appreciation.