An LED is placed in the circuit pictured below. You would like to choose a resistor value for R2 such that the current through the diode is 20mA. If the forward bias threshold voltage for your diode is 3 and the input voltage to the circuit is 4, what should the resistance be in ohms

The starship enterprise is caught in a time warp and spock is forced to use the primitive techniques of the 20th century to determine the specific heat capacity of an unknown mineral. the 125-g sample was heated to 96.3°c and placed into a calorimeter containing 85.9 g of water at 20.0°c. the heat capacity of the calorimeter was 14.2 j/k. the final temperature in the calorimeter was 24.5°c. what is the specific heat capacity (in j/g°c) of the mineral? enter to 4 decimal places.