full out output voltage??

I am just starting but I'm having a problem with using outputs to activate a 5vdc relay coil. I am only using the first practice program called blink to activate an output pin connected to a relay coil but am only getting about 2v (pin 10) and 3.5v (pin 13). I am using a 5vdc power supply plugged in to the round outlet on the arduino uno v3 and I can actuate the relay using only the voltage from the power supply. So what's the deal? Aren't outputs supposed to put out 5 volts when at high? Thanks in advance for your help in advance.

What is the coil resistance of the relay?

The chips used on an Arduino are only rated for a max of 40mA, but should generally be used at no more than about 25mA. Although you -can- draw more out, it will be at reduced voltage and may damaged the processor chip in the Arduino.

I doubt that you have a relay that takes only 20mA, so you are probably overloading the output pin. Use a driver MOSFET or Bipolar transistor. And you'll need a diode in parallel with the relay coil, wired cathode (pointy end) to the positive end, to absorb the spike produced when power is cut off from the relay coil.

Without the diode it is likely that the chip has been permanently damaged. Never switch
an inductive load without a free-wheel diode, as the numerous examples on these forums should show. Arduino Playground - HomePage

also, plugging less than 7V DC into the "round" power jack is not recommended, as it will likely be below the drop out voltage of the onboard regulator. You don't want to power your board that way.