1.2 SI Units | CIE A Level Physics Topic Questions 2025

1a

4 marks

Table 1.1 shows SI base quantities and their corresponding base unit.

Table 1.1

SI base quantity	SI base unit
Mass	kilogram, kg
Time
Length

(i)

Complete the missing SI base units for time and length in Table 1.1.

[2]

(ii)

Complete Table 1.1 by adding two other base quantities and their units.

[2]

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1b

2 marks

Newton's second law of motion describes the relationship between force F mass m and acceleration a:

$F = m a$

The derived unit for force is the newton (N).

Use Newton's second law to write 1 N in SI units.

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1c

2 marks

The kinetic energy equation describes the relationship between energy E, mass, m, and velocity, v.

$E_{k} = \frac{1}{2} m v^{2}$

The derived unit for energy is the joule (J).

Use the equation linking kinetic energy and speed to write 1 J in SI base units.

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1d

2 marks

The derived unit for power P is the watt W.

Given that power is the energy transferred E per unit time t, deduce the SI base units for power

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1a

8 marks

Convert the following measurements

(i)

42 km³ into mm³

[2]

(ii)

25 light-years into nm

[3]

(iii)

0.05 kWh into PeV

[3]

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1b

3 marks

The frequency f of a stationary wave on a string is given by

$f^{k} = \frac{T}{4 m L^{2}}$

where L is the length of the string, T is the tension in the string, m is the mass per unit length of the string and k is a dimensionless constant.

By considering the homogeneity of the equation, determine the value of k.

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1c

4 marks

The current $I$ through a semiconductor diode given by

$I = I_{0} e^{- \frac{q V}{n T}}$

where $I_{0}$ is the initial current, q is the charge of an electron, V is the applied potential difference, T is the temperature and n is a constant.

(i)

By considering the homogeneity of the equation, determine the units of n.

[3]

(ii)

Use the datasheet to determine the name of this constant.

[1]

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1a

6 marks

Define the following quantities and state their SI base units

(i)

velocity

[2]

(ii)

acceleration

[2]

(iii)

density

[2]

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1b

2 marks

The pressure $P$ due to a liquid of density $ρ$ is related to the depth $h$ by the expression

$P = ρ g h$

where $g$ is the acceleration of free fall.

Use this expression to determine the derived units of pressure $P$ .

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1c

3 marks

The speed $v$ of a sound wave through a gas of pressure $P$ and density $ρ$ is given by the equation

$v = \sqrt{\frac{γ P}{ρ}}$

where $γ$ is a constant.

Show that the constant $γ$ has no unit.

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Prefix	Power of ten
tera
	10⁹
	10³
centi	10⁻²
milli
micro
	10⁻⁹
pico	10⁻¹²

Quantity	Name	Symbol
length
	kilogram
		s
	ampere
temperature		K

SI Units (CIE A Level Physics)

Topic Questions