3.8 Power

Question 2

Define energy in the context of physics.

Answer 2

Energy is the capacity to do work or transfer heat.

Question 3

What are the two main types of energy?

Answer 3

• Kinetic energy
• Potential energy

Question 4

What is kinetic energy?

Answer 4

The energy stored in a moving body, transferred during its acceleration.

Question 5

What is potential energy?

Answer 5

The energy stored by a system which may later be transferred to another energy store.

Question 6

List examples of potential energy stores.

Answer 6

• Gravitational potential energy
• Elastic potential energy
• Electrical potential energy
• Chemical potential energy

Question 7

What is the definition of work in mechanical systems?

Answer 7

A measure of the energy transferred when a force is applied over a distance.

Question 8

How is work done measured?

Answer 8

In joules (J).

Question 9

What is one joule equivalent to in terms of force and distance?

Answer 9

One joule is the work done when a force of one newton moves a mass over one metre.

Question 10

In electrical systems, how is work defined?

Answer 10

The energy transferred when an electric charge is moved between two points in a circuit.

Question 11

What unit is used to measure potential difference?

Answer 11

Volts (V).

Question 12

Fill in the blank: Power is the rate at which _______ is done or heat is transferred.

Answer 12

work

Question 13

What is the unit of power?

Answer 13

Watts (W) or joules per second (J/s).

Question 14

How is electrical power defined?

Answer 14

The number of joules of energy transferred to or from a circuit in one second.

Question 15

What is the difference between direct and indirect measurement of electrical power?

Answer 15

• Direct measurement: Using a wattmeter
• Indirect measurement: Using a voltmeter and an ammeter

Question 16

What is the function of a voltmeter?

Answer 16

To measure potential difference across components in parallel.

Question 17

What is the function of an ammeter?

Answer 17

To measure current in series.

Question 18

True or False: Power remains constant over time for AC devices.

Answer 18

False

Question 19

What does potential difference measure?

Answer 19

The electrical potential energy available per coulomb of charge.

Question 20

What happens when a current flows through a resistor?

Answer 20

Energy is transferred from the electric circuit to the thermal energy store of the resistor

Question 21

What is the work done by the electric circuit in relation to a resistor?

Answer 21

Transferring energy to the resistor and increasing the resistor’s temperature

Question 22

How does heat flow from a resistor to the surroundings?

Answer 22

Through conduction, convection, and radiation

Question 23

What happens to the heat generated by all components in a circuit?

Answer 23

It is dissipated into the air around the components

Question 24

What is the rate at which heat is dissipated called?

Answer 24

Power, measured in watts (W)

Question 25

True or False: Resistors are designed to dissipate power.

Answer 25

True

Question 26

What limits the maximum power that a particular resistor can dissipate?

Answer 26

The resistor's design and specifications

Question 27

What can happen if the power dissipated exceeds the resistor's limit?

Answer 27

* The value of the resistor may rise beyond its stated tolerance * The resistor may melt (burn out and fuse) * The resistor may start a fire

Question 28

Why is it important to observe the correct power rating when designing circuits?

Answer 28

To ensure the circuit functions correctly and to prevent hazards

Question 29

Fill in the blank: The heat generated by a resistor flows to the surroundings through _______.

Answer 29

conduction, convection, and radiation

Question 30

What is electric power?

Answer 30

The rate at which work is done or energy is transformed into an electrical circuit

Question 31

What is the formula for electric power?

Answer 31

P = VI

Question 32

In the formula P = VI, what does P represent?

Answer 32

Power in watts (W)

Question 33

In the formula P = VI, what does V represent?

Answer 33

Potential difference in volts (V)

Question 34

In the formula P = VI, what does I represent?

Answer 34

Electric current in amperes (A)

Question 35

What is the power consumption when the current is 1 ampere and the voltage is 1 volt?

Answer 35

1 watt

Question 36

If a hydraulic pump has a voltage of 230 V and a current of 4 A, what is its power consumption?

Answer 36

920 W

Question 37

Fill in the blank: Power is the product of _______ and _______.

Answer 37

voltage, current

Question 38

True or False: The unit of power is measured in watts.

Answer 38

True

Question 39

What is the relationship between voltage, current, and power?

Answer 39

Power is calculated by multiplying voltage and current

Question 40

What is electrical power (P)?

Answer 40

The rate at which work is done or the rate of conversion of energy by an electrical system. ## Footnote Power can also be expressed in terms of voltage and current.

Question 41

What is the formula for power?

Answer 41

Power = work done (joules) / time taken (seconds). ## Footnote This relationship shows how power relates to work and time.

Question 42

What is the SI unit of power?

Answer 42

Watt (W), which is defined as 1 joule per second. ## Footnote The watt is a measure of electrical power.

Question 43

How can electrical power be expressed using voltage and current?

Answer 43

P = V x I ## Footnote This expression is derived from Ohm's Law where V = IR.

Question 44

What happens to power if voltage is halved?

Answer 44

Only a quarter of the power is obtained. ## Footnote This is due to the relationship P ∝ V².

Question 45

What happens to power if voltage is doubled?

Answer 45

The power is four times larger. ## Footnote This follows the same principle of P ∝ V².

Question 46

How can power be calculated if resistance is known?

Answer 46

P = I²R or P = V²/R ## Footnote These formulas allow calculation of power without direct current measurement.

Question 47

What is electrical work?

Answer 47

Work done when a charge is moved between two points at different electrical potentials. ## Footnote The formula for electrical work is W = Q x V.

Question 48

What is the SI unit of work?

Answer 48

Joule (J). ## Footnote One joule of work is done when one coulomb moves through a potential difference of one volt.

Question 49

What is the formula for electrical work?

Answer 49

Electrical Work (joule) = Charge (coulomb) x Potential Difference (volt). ## Footnote This shows the relationship between charge and electrical potential.

Question 50

What is electrical energy?

Answer 50

The ability of an electrical system to do work. ## Footnote Energy used is equal to the work done, with both measured in joules.

Question 51

What does the Law of Conservation of Energy state?

Answer 51

Energy can neither be created nor destroyed but can be changed from one form to another. ## Footnote This law emphasizes the transformation of energy rather than its disappearance.

Question 52

What is the multiplier for the prefix 'mega'?

Answer 52

1 000 000 (10^6). ## Footnote Mega is commonly used in measuring large quantities.

Question 53

How do you convert from low to high exponents in unit conversion?

Answer 53

Shift the decimal point to the left. ## Footnote This method is essential for accurate unit conversions.

Question 54

How do you convert from high to low exponents in unit conversion?

Answer 54

Shift the decimal point to the right. ## Footnote This is the opposite action of converting from low to high exponents.

Question 55

Fill in the blank: The energy a body contains may be determined by calculating the ______ done on the body.

Answer 55

work ## Footnote This reflects the relationship between energy and work done.

Question 56

What is the result of converting 125 microamperes to amperes?

Answer 56

0.000125 ampere. ## Footnote This conversion illustrates the process of shifting the decimal point.

Question 57

What is the result of converting 1 kW to watts?

Answer 57

1 000 W. ## Footnote This demonstrates the conversion from kilowatts to watts by shifting the decimal point.