Question

manipulating the strength of an electromagnet
simple electromagnet
predict what would happen to the strength of the
iron nail
coiled wire
electromagnet in each situation.
using a battery with a higher voltage:
wire
wrapping the wire around the nail only three times:
changing the direction of the current by reversing the
battery connections:
using a plastic stick in place of the iron nail:
battery
holding the nail vertically rather than horizontally:

Explanation:

Step1: Analyze the effect of voltage

According to Ohm's law \(I=\frac{V}{R}\) (where \(I\) is current, \(V\) is voltage and \(R\) is resistance). If resistance \(R\) of the circuit (due to wire etc.) is constant, higher voltage \(V\) means higher current \(I\). The strength of an electromagnet is proportional to the current passing through the coil. So, higher current increases the strength.

Step2: Analyze the effect of number of turns

The strength of an electromagnet is proportional to the number of turns \(N\) of the coil (\(B\propto N\) for a solenoid - like electromagnet here). Fewer turns (three times instead of more) decrease the strength.

Step3: Analyze the effect of current direction

The direction of current affects the polarity (north - south orientation) of the electromagnet, not its strength. So, reversing the battery connections (changing current direction) has no effect on strength.

Step4: Analyze the effect of core material

Iron is a ferromagnetic material which enhances the magnetic field of the electromagnet. Plastic is a non - magnetic (diamagnetic/paramagnetic but not ferromagnetic) material. Using plastic instead of iron reduces the strength (as there is no ferromagnetic enhancement).

Step5: Analyze the effect of orientation

The orientation (vertical or horizontal) of the nail (core) does not affect the magnetic field strength (which depends on current, number of turns and core material) in a significant way for a simple electromagnet setup like this. So, no effect on strength.

Answer:

Using a battery with a higher voltage: The strength of the electromagnet increases.
Wrapping the wire around the nail only three times: The strength of the electromagnet decreases.
Changing the direction of the current by reversing the battery connections: The strength of the electromagnet remains the same.
Using a plastic stick in place of the iron nail: The strength of the electromagnet decreases.
Holding the nail vertically rather than horizontally: The strength of the electromagnet remains the same.