DTW TUTORIALS - PHYSICS; Measurement and Units

PHCN measures its electrical energy in- A. Wh B. J C. W D. kWh

• A
• B
• C
• D

Answer explanation

ANSWER IS D.
The Power Holding Company of Nigeria (PHCN) measures its electrical energy in kilowatt-hours (kWh). This is because the kilowatt-hour is a unit of energy equivalent to one kilowatt (1 kW) of power expended for one hour of time.

What is the least possible error encountered when taking measurement with a meter rule? A 0.5mm B 0.2mm C 0.1 mm D 1.0 mm

• A
• B
• C
• D

Answer explanation

ANSWER: A

EXPLANATION

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Note that the error in any measurement is given as half of the smallest scale division (accuracy)

The accuracy of a metre rule is 1.0mm

∴ The uncertainty (error) in any measurement involving a metre rule = 1/2(1.0mm) = 0.5mm

The instrument used for accurate measurement of the internal and external diameters of a pipe is the -

A. vernier callipers B. micrometer C. spherometer D. metre rule

• A
• B
• C
• D

Answer explanation

ANSWER: A

EXPLANATION

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Vernier callipers is best used for the accurate measurement of the internal and external diameter of a pipe.

A spring balance measures
I. the mass of the body hung on it
II. the earth's gravitational pull on the body hung on it
III. the weight of the body hung on it.
Which of the above statements is (are) correct?

A. I only B. III only C. II and III only D. I, II and III

• A

• B

• C

• D

Answer explanation

ANSWER: C

EXPLANATION

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A spring balance indicates the extension in a spring due to the weight (or gravitational pull) of a body hung on it. [The reading on a spring balannce will vary, for instance with altitude even though the mass of the body is constant]

Which of the following is not fundamental?

A. kelvin B. steradian C. candella D. mole

• A

• B

• C

• D

Answer explanation

ANSWER: B

EXPLANATION

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Steradian is not a fundamental unit. It is a derived unit in the International System of Units (SI) for measuring solid angles. The other options, Kelvin, Candella, and Mole, are fundamental units in the SI system.

A chemical balance is used for measuring

A. volume B. mass C. thickness D. density

• A

• B

• C

• D

Answer explanation

ANSWER: B

EXPLANATION

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A chemical balance is used for measuring mass. It is a type of balance designed to measure small mass in the sub-milligram range. The measuring pan of the balance is inside a transparent enclosure with doors so that dust does not collect and so any air currents in the room do not affect the balance's operation.

Which of the following is not a derived unit?

A. Newton B. Watt C. Joule D. Second

• A

• B

• C

• D

Answer explanation

ANSWER: D

EXPLANATION

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In physics, there are two types of units: base units and derived units. Base units are the fundamental units and cannot be broken down into simpler units. Derived units are formed by combining base units. Newton, Watt, and Joule are all derived units. Newton is the unit of force, Watt is the unit of power, and Joule is the unit of energy. Second, on the other hand, is a base unit. It is the base unit of time in the International System of Units.

What is the unit for measuring the amplitude of a sound?

A. Decibel B. Coulomb C. Flux D. Cycles

• A

• B

• C

• D

Answer explanation

ANSWER: A

EXPLANATION

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The amplitude of a sound is measured in Decibels (dB). Decibel is a logarithmic unit used to express the ratio of two values of a physical quantity, often power or intensity. It is commonly used in acoustics to quantify sound levels.

The dimension of Newton's gravitational constant M^xL^yT^z , the value of x+y/z is

A. 1 B.-1 C.2 D. -2

• A

• B

• C

• D

Answer explanation

ANSWER: B

EXPLANATION

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Recall: From Newton's Law of Universal Gravitation

F = GM₁M₂/r²

G = Fr²/M₁M₂

G = MLT^-2×L²/M²

G = M^-1L³T^-2
Equate this to M^xL^yT^z
M^xL^yT^z = M^-1L³T^-2
x = -1, y = 3 and z = -2

x+y/z

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-1+3/-2

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2/-2

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-1

The unit cycle per second is the same as

A. watt B. metres per second C. hertz D. radians per second

• A

• B

• C

• D

Answer explanation

ANSWER: C

EXPLANATION

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The unit 'cycle per second' is the same as 'hertz'. Both are units of frequency, which measures the number of occurrences of a repeating event per unit of time. The term 'cycle per second' was largely replaced by 'hertz' in the 1960s.