Arduino Questions and Answers – LDR Sensor

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This set of Arduino Multiple Choice Questions & Answers (MCQs) focuses on “LDR Sensor”.

1. What is the use of the LDR Sensor?
a) Monitors Motion
b) Monitors air pressure
c) Monitors Light Intensity
d) Monitors heartbeat
View Answer

Answer: c
Explanation: An LDR Sensor is used to measure the light intensity of the space surrounding it. Similar variations of these kinds of sensors are used in phones which allow manufacturers to turn off the screen when you place your phone to your ear during a call.

2. How many pins are present in the LDR Sensor?
a) 1
b) 4
c) 2
d) 5
View Answer

Answer: c
Explanation: The LDR is a passive sensor, which means it does not require any external voltage supply for it to run. So it only has two terminals which are to be connected in parallel for maximum performance and so that if the LDR becomes defunct, it does not affect the working of the entire circuit.

3. What is the full form of the LDR Sensor?
a) Lithium Diode Resistor
b) Light Diaphragm Resistor
c) Lithium Disk Resistor
d) Light Dependent Resistor
View Answer

Answer: d
Explanation: An LDR is called a Light Dependent Resistor. It is also called a photo-resistor or a cadmium sulfide cell. It is a photocell that works on the principle of photo-conductivity. It’s resistance value decreases when the intensity of light decreases and vice-versa.
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4. What will happen if we supply a voltage of 250 kV to the terminal of the LDR Sensor?
a) Damage is caused
b) Module will shut down
c) Module will not respond for the time the voltage is applied
d) Module will function normally
View Answer

Answer: a
Explanation: The LDR Sensors are mostly built to work on a voltage range that is not too high and should not be used for high power usage as it will burn up. Any voltage lower than that and the sensor will not be able to power on, but however any voltage significantly above that and the sensor may suffer permanent damage.

5. Which of the formulae give us the relation between resistance and illumination in the LDR Sensor?
a) Resistance = Constant_1 * (Illumination^Constant_2)
b) Resistance = Constant_1 * (Illumination+Constant_2)
c) Resistance = Constant_1 ^ (Illumination-Constant_2)
d) Resistance = Constant_1 + (Illumination^Constant_2)
View Answer

Answer: a
Explanation: Constant_1 * (Illumination^Constant_2) gives the correct relation between the resistance and the illumination in the LDR sensor. Here the SI unit of resistance is Ohms and that of Illumination is Lux.

6. Which one of the following materials would be used for making an LDR?
a) Lead Sulfide
b) Pure Aluminum
c) Iron Ore
d) Aluminum Oxide
View Answer

Answer: a
Explanation: What the LDR needs is a semiconductor. So that when some light having enough energy strikes on it, more electrons are excited to the conduction band which results in large number of charge carriers which in turn results in current flowing through it when the circuit is closed.

7. What kind of sensor is the LDR Sensor?
a) Passive
b) Active
c) Radio
d) Pressure based
View Answer

Answer: a
Explanation: The LDR sensor is a passive sensor since it requires no external supply of voltage in order for it to work. It simply acts as a variable resistor and changes the resistance of itself while light of varying intensity falls on it.
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8. If an LDR is connected to an LED and a battery and is brought from the dark to the light, what will be the state of the LED?
a) Lit
b) Not lit
c) Damaged by voltage change
d) Damaged by power surge
View Answer

Answer: a
Explanation: The resistance of an LDR depends upon the amount of light that is incident on it. So greater the light intensity, lesser is it’s resistance, and so greater is the current flowing through to the LED making it brighter.

9. Do LDR’s respond to all wavelengths of light?
a) Yes
b) No
View Answer

Answer: b
Explanation: LDR’s are non linear devices. Their sensitivity varies with the wavelength of light that’s incident on them. Some LDR’s might not response to a certain range of wavelengths at all depending upon the kind of material used in different devices, which consequently have different spectral response curves.
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10. How much time on an average does the LDR take for it’s resistance to change when light is incident?
a) 8 to 12 ms
b) 12 min
c) 30 s
d) 354 hr
View Answer

Answer: a
Explanation: 8 to 12ms is the correct value of the time that an average LDR takes for its resistance to change in response to the light incident on it. It also takes about a second approximately for the resistance to rise back up to its initial value when no light is incident.

Sanfoundry Global Education & Learning Series – Arduino.

To practice all areas of Arduino, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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