Read the case study given below and answer the questions that follow.
A student investigates the strength of an electromagnet by winding insulated copper wire around an iron nail and connecting it to a battery to compare the electromagnet's strength.
The student wants to make an electromagnet stronger. He repeats the activity by increasing the number of cells in one trial and increasing the number of turns of the coil in another trial. In both trials, he compares the deflection of the compass needle and the number of paper clips attracted.
1. Which change will make the electromagnet stronger?
2. Which observation indicates that the electromagnet has become stronger?
3. Which factor increases the current flowing through the coil?
4. Which statement best summarises the activity?