Fig. 1 shows a simple electromagnetic launcher used for a physics demonstration. A short iron projectile rests just before a solenoid. A capacitor supplies ...
Question 1 Report
Fig. 1 shows a simple electromagnetic launcher used for a physics demonstration. A short iron projectile rests just before a solenoid. A capacitor supplies a brief, large current to the coil when a push button is pressed. The coil attracts the projectile towards its centre. A light gate measures the time taken by the projectile to travel 0.40 m after leaving the coil. The teacher uses a plastic safety screen and never allows students to stand in front of the launcher.
(a) What happens to the projectile when the current starts? [1]
(b) Which material should not be used for the projectile: iron or aluminium? [1]
(c) When the projectile reaches the centre of the coil, what change should be made to the current to prevent it being pulled back? [1]
(d) Sketch one way to increase the launch force. [1]
(e) What is the average speed if the measured time is 0.20 s? [2]
Answer Details
A current in the solenoid makes it an electromagnet. Iron is attracted into the region of strongest magnetic field, near the centre of the coil.
- (a) The projectile is attracted into the solenoid, so it accelerates forwards. [1]
- (b) Aluminium should not be used. Iron is magnetic and is strongly attracted by an electromagnet, whereas aluminium is not suitable here. [1]
- (c) The current should be switched off when the projectile reaches the centre. Otherwise the electromagnet could attract it back towards the centre. [1]
- (d) Increasing the current, adding more turns to the coil, or using a stronger power supply increases the magnetic field and therefore the launch force. [1]
- (e) Average speed is found from \(v=\frac{d}{t}\):
\[v=\frac{0.40\ \text{m}}{0.20\ \text{s}}=2.0\ \text{m/s}\]Average speed = 2.0 m/s. [2]
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