8051 Microcontroller Questions and Answers – Interfacing with Motors

This set of 8051 Micro-controller Multiple Choice Questions & Answers (MCQs) focuses on “I/O Port Programming and Addressing Modes”.

1. What is the principle on which electromagnetic relays operate?
a) electromagnetic induction
b) motor control
c) switching
d) none of the mentioned
View Answer

Answer: a
Explanation: Electromagnetic relays work on the principle of electromagnetic induction. It is used as a switch in industrial controls, automobile and appliances. It allows the isolation of the sections of a system with two different voltage sources.

2. What are DPDT relays?
a) Single pole, single throw
b) Single pole, double throw
c) Double pole, double throw
d) None of the mentioned
View Answer

Answer: c
Explanation: In DPDT relay, there are two poles and two throws (i.e.contacts). For each pole there are two contacts i.e. normally open (NO) and normally closed (NC). The contacts can be NO or NC. Generally, contact is NC when the coil is not energized. When the coil is energized both poles become NC.

3. Why do we need a ULN2803 in driving a relay?
a) for switching a motor
b) for increasing the current
c) for increasing the power
d) for switching the voltage
View Answer

Answer: b
Explanation: We need a ULN2803 for driving a relay because the relay coil requires 10mA or more current to be energized. If microcontroller pins are not able to provide sufficient current to drive relays then we need ULN2803 for driving relays.

4. Why are solid-state relays advantageous over electromechanical relays?
a) they need zero voltage circuit
b) they need less current to be energised
c) they need less voltage to be energised
d) none of the mentioned
View Answer

Answer: b
Explanation: Solid-state relays are advantageous over electromechanical relays because their switching response time is much faster than electromechanical relays as solid-state relays are made-up of semiconductor materials. Also, solid-state relays required low input current for operation and small packaging make them ideal for microcontrollers.

5. What are optoisolators?
a) it is a driver
b) it is a thing isolated from the entire world
c) it is a device that can be used as an electromagnetic relay without a driver
d) none of the mentioned
View Answer

Answer: c
Explanation: Optoisolators are devices that can be used as an electromagnetic relay without a driver. It usually consists of a led (transmitter) and a photoresistive receiver.
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6. How can we control the speed of a stepper motor?
a) by controlling its switching rate
b) by controlling its torque
c) by controlling its wave drive 4 step sequence
d) cant be controlled
View Answer

Answer: a
Explanation: Speed of a stepper motor can be controlled by changing its switching speed or by changing the length of the time delay loop.

7. Which of the following can be a unit for torque?
a) kg/m2
b) ounce-inch
c) kg-m3
d) g/m
View Answer

Answer: b
Explanation: Torque is equal to the force applied at a particular distance. So its unit can be ounce-inch.

8. The RPM rating given for the DC motor is for?
a) no-loaded
b) loaded
c) none of the mentioned
d) all of the mentioned
View Answer

Answer: a
Explanation: RPM rating given for a DC motor is for a no-loaded condition.

9. How can we change the speed of a DC motor using PWM?
a) By changing amplitude of PWM
b) By keeping fixed duty cycle
c) By changing duty cycle of PWM
d) By increasing power of PWM
View Answer

Answer: c
Explanation: We can change the speed of a DC motor using PWM by changing the duty cycle of PWM. Changing duty cycle means changing ON and OFF timing of PWM. Even if amplitude of PWM is fixed by increasing the ON time of PWM increases the speed of the DC motor.

10. How can the direction of the DC motor be changed?
a) by changing the torque
b) by changing the switching speed
c) by changing the polarity of voltages connected to the leads
d) by changing the RPM rating
View Answer

Answer: c
Explanation: The direction of the DC motor can be changed by changing the polarity of the voltages connected to its leads.

Sanfoundry Global Education & Learning Series – Microcontroller.

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

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Manish Bhojasia - Founder & CTO at Sanfoundry
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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