Electric motors and change in flux "When a current passes through an electric motor, the magnetic force on the motor causes a torque on the loop of wire causing it to turn".  However, when the loop rotates, there should also be a change in magnetic flux causing an induced emf (Faraday's law). However, my book makes no such reference. 
my questions:


*

*Is there going to be an induced emf opposing the applied emf of the DC source in the electric motor?

*If yes, wouldn't the induced emf cancel the applied emf causing no magnetic force to be exerted and thus no longer converting electrical energy to mechanical energy?

 A: Yes, there is an induced EMF called "Back EMF" or "Counter EMF". This is proportional to the rate of rotation of the coil; the higher the velocity of the coil the higher the counter induced EMF. 
The counter EMF can be calculated by subtracting the impressed voltage ($V$) in the coil from the supply EMF coming from the power source:
$e = E - IR$, and $V = IR$. 
Where, the supply EMF is: $E$, the back EMF is: $e$, the resistance of the coil is: R and the current through the coil is: $I$.
-Since ($e$) is proportional to the angular speed ($\omega$ ) the greater $\omega$ the smaller $I$.
There must be slightly more impressed voltage than Back EMF, to allow enough current to flow, to overcome frictional losses. Once a load is added, all this goes out the window, because the motor slows down, reducing the Back EMF, and allowing greater current to flow, and greater power developed to drive the load. 
If a motor has zero friction losses, the maximum velocity can be achieved when the counter EMF is equal to the supply EMF. 
A simple test you could perform at your car: With the window closed, lift the switch of the electric window in your car that is running at idle, and hold it momentarily and notice the idle RPM drop. The electric motor in the door is stationary and therefore the inrush current will be very high. The alternator will try to provide for the large current which subsequently drags down the engine. As soon as the power window motor overcomes its inertia and starts spinning, back EMF will be produced, exerting less load on the alternator. Hence, the engine speed will return to the normal operation. (Wikipedia)
A: I believe you are correct to assume that and it is called back emf. Modern day motors have corrected for this (or minimized it). The back emf is always smaller than the applied, or should be if you want it to rotate and produce power.
