A warehouse uses a relay so that a low-current magnetic door sensor can switch a brighter warning lamp. Fig. 1 shows the separate control and lamp circuits....
Question 1 Report
A warehouse uses a relay so that a low-current magnetic door sensor can switch a brighter warning lamp. Fig. 1 shows the separate control and lamp circuits. When the door is shut, the sensor switch is closed and current flows in the relay coil.
(a) State the component inside the relay box that becomes an electromagnet. [1]
(b) Explain how closing the sensor switch causes the lamp circuit to become complete. [3]
(c) Calculate the power of the lamp when the current in its circuit is 0.50 A. [2]
(d) Describe one advantage of using a relay in this system. [2]
(e) State what happens to the lamp when the door is opened. [2]
Answer Details
(a) The coil inside the relay becomes an electromagnet [1].
(b) Closing the sensor switch allows current to flow through the relay coil [1]. The coil becomes an electromagnet [1], which attracts or moves the contacts so that the lamp circuit is completed [1]. The control circuit and lamp circuit are separate.
(c)
\[P=VI=12\text{ V}\times0.50\text{ A}=6.0\text{ W}\]
The lamp power is \(6.0\text{ W}\) [2].
(d) A relay allows the low-current sensor circuit to control a higher-current lamp circuit [1], while keeping the two circuits electrically separate and protecting the sensor [1].
(e) When the door opens, the sensor switch opens and current stops in the relay coil [1]. The contacts open, breaking the lamp circuit, so the lamp goes off [1].
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