Question

How does the magnitude of the lever arm will change if you decrease the angle?

Answer 1

Answer: It decreases.

Explanation:

Lever arm is defined as the "perpendicular distance that exists from the rotation axis to the line of action of the force". Being its magnitude $(Nm)$ related to the application of the force that produces a torque.  

To understand it better:  

The lever arm is an effective distance to apply a force with respect to a certain point, and this distance serves as an effective applied force amplification factor.

In this sense, Torque $\tau$ is defined as:

$\tau=rFsin \theta$

Where:

$r$ is the distance from the applied force to the fulcrum

$F$ is the applied force

$\theta$ is the angle between $r$ and $F$

It is important to note, $\tau$ is maximum when $\theta=90\°$. Then, assuming $r$ and $F$ remains the same, if $\theta$ decreases $\tau$ decreases, as well.

Hence:

If the angle $\theta$ decreases, the magnitude of the lever arm will decrease.

So, the greater the lever arm, the greater the torque and the lesser the force we have to apply.