Understanding Density and Relative Density

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Questions and Answers

The slope of a graph plotting mass (m) against volume (V) for a substance represents which property?

  • Specific gravity
  • Density (correct)
  • Volume
  • Weight

Which of the following is a factor affecting the density of a substance?

  • The color of the substance
  • The atomic weight (correct)
  • The ambient pressure
  • The shape of the container

What is the dimensional formula for density?

  • $MLT^{-2}$
  • $M^{-1}L^{3}T^{0}$
  • $ML^{-3}T^{0}$ (correct)
  • $M^{2}L^{-3}T^{0}$

If you mix two liquids with densities $\rho_1$ and $\rho_2$ and volumes $V_1$ and $V_2$ respectively, what is the density of the mixture, assuming the volumes are additive?

<p>$(\rho_1V_1 + \rho_2V_2)/(V_1 + V_2)$ (B)</p>
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How is the relative density of a substance defined in terms of its density and the density of water?

<p>The ratio of the substance's density to the density of water. (C)</p>
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The relative density of a material is measured under which condition?

<p>Same temperature (C)</p>
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What is the relationship between the mass of a material and its density when the volume is kept constant?

<p>Density increases as the mass increases. (B)</p>
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Given a mixture of 50 $m^3$ of water with a density of 1000 $kg/m^3$ and 40 $m^3$ of liquid with a density of 790 $kg/m^3$, what is the density of the resulting mixture?

<p>911 $kg/m^3$ (A)</p>
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If the relative density of a certain type of wood is 0.6, what is the density of this wood in $kg/m^3$?

<p>600 (D)</p>
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If the relative density of a piece of wood is 0.6, then what is the mass of a 0.1 $m^3$ piece of this wood?

<p>60 kg (A)</p>
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The average force acting perpendicularly on a unit area surrounding a point is the definition of what?

<p>Pressure (D)</p>
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The pressure exerted by a force $F$ acting on an area $A$ at an angle $\theta$ to the area's normal is given by:

<p>$P=F cos(\theta)/A$ (D)</p>
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What are the dimensions of pressure?

<p>$ML^{-1}T^{-2}$ (A)</p>
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If several surfaces with different areas are subjected to different forces, on which surface is the pressure exerted the maximum?

<p>Force = 3/2 F, Area = 1/2 A (B)</p>
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A fish tank with a base area of 1000 $cm^2$ contains water with a weight of 4000 N. If the tank is placed on a horizontal surface, calculate the pressure of the water at the bottom of the tank.

<p>4 x $10^4$ $N/m^2$ (B)</p>
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A force of 15 N acts on an area of 2 $cm^2$ at an angle of 30° with respect to the normal. What is the pressure exerted on the area?

<p>64.95 x $10^3$ $N/m^2$ (D)</p>
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What is the formula for calculating the pressure at a certain depth inside an open container with liquid.

<p>$P = pgh + P_a$ (D)</p>
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The force exerted by a liquid on the bottom of a container depends on which factors?

<p>Area of the bottom of the container, liquid density and depth (B)</p>
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In analyzing the pressure at different points inside a lake, the graph represents the relation between the pressure (P) and depth (h). What does the value at h=0 represent?

<p>Atmospheric pressure (A)</p>
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If you analyze the pressure at different points inside a lake and graph it, what does the slope of the graph represent if you plot pressure (P) against depth (h)?

<p>The density of water (A)</p>
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The pressure at the bottom of a high dam depends on which factor?

<p>Depth of the water (C)</p>
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Which of the following graphs represents the total external pressure acting on a submarine at different depths below the surface of the sea?

<p>A graph starting at atmospheric pressure and increasing linearly. (B)</p>
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Connecting vessels are an application of pressure, which of the following is true for them?

<p>Liquids level at the same horizontal level (B)</p>
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A U-tube includes two liquid, one of them being water. What statement is true for the relative density?

<p>The density is the ratio of the height of water to the liquid height (D)</p>
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In a barometer, what variables can be used to approximate the height of a mountain?

<p>The mercury pressure, the air pressure, the gravity, and the height of the barometer (B)</p>
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Which of the following increases the height above sea level?

<p>The atmospheric pressure will decrease (C)</p>
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If you submerge a capillary tube in water, what factor will affect the pressure inside?

<p>The atmospheric pressure and water height (B)</p>
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What is measured using a manometer?

<p>Enclosed gas pressure (A)</p>
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In a mercury manometer, what happens to the pressure if the liquid level in the free end branch changes compared to the level on the other side?

<p>The pressure changes if the liquid used is mercury (B)</p>
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The height in two liquids are different when at equilibrium inside a U-shaped tube, so what can you infer about its densities?

<p>The ratio of the height is a function of the density (D)</p>
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When is Pascal's Principle applicable?

<p>For liquids and gases in closed systems (D)</p>
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In hydraulic presses, what quantity is being multiplied?

<p>Force (A)</p>
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In an ideal hydraulic press with pistons at the same horizontal level, how does the force produced at the big piston compare to the force acting on the small piston?

<p>Greater than one (C)</p>
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If the radii are 8/3, what is the work due to the motion?

<p>1 (B)</p>
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What best describes Boyles Law

<p>pressure is inversely proportional to the volume (B)</p>
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If the volume of a gas is 2 liters at 2 atm, what does it become when the pressure decreases to 1 atm at a constant temperature?

<p>4 liters (D)</p>
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An amount of gas of volume 350 $cm^3$ at a pressure of 2 atm is expanded, what is the volume at 1 atm?

<p>700 $cm^3$ (C)</p>
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A gas has an initial density of 32 g/L when the pressure is at 760 mm Hg. If pressure is decreased to 570 mm Hg, what does its density become?

<p>24 g/L (A)</p>
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What best described Charle's law?

<p>volume changes with temperature (A)</p>
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Where does the volume stay constant?

<p>At Pressure Law (A)</p>
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If an amount of gas is 450 $cm^3$ at a temperature of 273 K, what volume does it measure at 364K?

<p>600 $cm^3$ (C)</p>
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What best describes volume expansion?

<p>a volume coefficient at constant pressure equilibrium (C)</p>
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If the pressure of a quantity of gas is 59.8 cm Hg, what is the pressure if the volume stays constant?

<p>80.6 cm Hg (B)</p>
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In the context of gas laws, what does the general gas law describe?

<p>The relationship between pressure, volume, and temperature of a fixed amount of gas (B)</p>
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The volume of a gas at 27°C under a pressure of 60 cm Hg is 380 cm. Find its volume at the (STP)

<p>333 $cm^3$ (A)</p>
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If you graph two equal masses of the same gas, what do you infer knowing if volume 1 is greater than volume 2?

<p>volume 1 is less than volume 2 (B)</p>
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Flashcards

Density

Mass per unit volume of a substance.

Slope of Density Graph

The change in mass divided by the change in volume on a graph.

Density of a Mixture

Density of a mixture is the total mass of the mixture divided by the total volume of the mixture.

Relative Density

Ratio of a material's density to the density of water at the same temperature.

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Pressure

Average force acting perpendicular to a surface per unit area.

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Pressure in a Liquid (Open)

Pressure at a depth in a liquid open to the air

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Pressure in a Liquid (Closed)

Pressure at a depth in a closed liquid

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Force Exerted on Container Bottom

To calculate the force exerted by a liquid on the bottom.

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Barometer

The devices used to measure atmospheric pressure.

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Pressure in Horizontal Plane

At all points in the same horizontal plane in a Static homologous liquid the pressure is the same.

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Pascal's Principle

The change in pressure divided by the original pressure

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Hydraulic Press

Device that uses fluid to multiply force.

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Hydraulic Press Advantage

The mechanical advantage given by the ratio of piston areas in a hydraulic press.

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Boyle's Law

Volume of a fixed gas is inversely proportional to its pressure.

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Charles's Law

Volume of a fixed gas is directly proportional to its temperature (in Kelvin).

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Pressure Law

Describes how pressure and temperature are related when volume is constant.

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General Gas Law

Relates pressure, volume, and temperature of a fixed amount of gas.

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Study Notes

Density

  • Density is the mass per unit volume of a substance
  • Density is represented by ρ and Volume is represented by Vol
  • The mathematical relation for density is ρ = m / Vol
  • Density is a scalar quantity
  • The measuring unit for density is Kg/m³
  • The dimensional formula for density is ML⁻³T⁰

Graph of Density

  • The slope of the graph (Δm / ΔVol) equals density (ρ)

Factors Affecting Density

  • Atomic weight or molecular weight
  • Distance between atoms or molecules

Density Equations

  • m_mix = m₁ + m₂ + ...
  • ρ_mix(V_ol)_mix = ρ₁(V_ol)₁ + ρ₂(V_ol)₂ + ...
  • (V_ol)_mix = (V_ol)₁ + (V_ol)₂ + ...

Volume Formulas

  • Sphere: V_ol = (4/3)πr³
  • Cylinder: V_ol = πr²h
  • Rectangular prism: V_ol = hlw

Relative Density

  • ρ_relative = (ρ_material) / (ρ_water) at the same temperature
  • ρ_relative = (m_material) / (m_water) at the same volume and temperature
  • ρ_relative = (W_material) / (W_water) at the same volume and temperature

Pressure

  • Pressure is the average force acting perpendicular to the unit area surrounding a point
  • The measuring unit for pressure is Pascal (Pa).

Pressure Equivalents

  • 1 Pascal (Pa) is equivalent to Kg⋅m⁻¹⋅s⁻²
  • 1 Pascal (Pa) is equivalent to N/m²
  • 1 Pascal (Pa) is equivalent to J/m³

Pressure Formulas

  • Force perpendicular to the area: P = F/A = mg/A
  • Force makes angle θ with the area: P = (F sin θ)/A
  • Force makes angle θ with the normal of area: P = (F cos θ)/A
  • A is the area

Pressure Dimensions

  • Pressure dimensions are ML⁻¹T⁻²

Pressure at a Point Inside a Liquid

  • Opened to air: P = ρgh + Pa
  • Closed: P = ρgh
  • ΔP/Δh = ρg, which represents the slope

Force Calculation in Liquids

  • Force at the bottom of the container: F = ρghA = ρgV_ol
  • Force on one of the vertical faces of the container: F = ρg * (1/2)hA = (1/2)ρghA = (1/2)ρgV_ol

Atmospheric Pressure

  • Atmospheric pressure is measured in Pascal (Pa).
  • Denoted as Pa.
  • It is directly proportional to average density of air and acceleration due to gravity
  • It is inversely proportional to temperature, and height above sea level
  • 1.013 × 10⁵ N/m² equals 1.013 × 10⁵ Pascal
  • 1.013 × 10⁵ N/m² equals to 1.013 bar
  • 1.013 × 10⁵ N/m² equals 1 atm
  • 1.013 × 10⁵ N/m² equals 0.76 mHg
  • 1.013 × 10⁵ N/m² equals 76 cmHg
  • 1.013 × 10⁵ N/m² equals 760 mmHg

Applications

  • Connecting vessels: Pa = PB = PC = PD = PE and ha = hB = hC = hD = hE
  • Mercury barometer: PA = PB = Pa and Pa = ρHgghHg

U-Tube Manometers

Structure of U-Tube

  • U-shaped tube

Idea Behind U-Tube

  • Pressure is the same at all points in the same horizontal plane in a static homogeneous liquid

Uses of U-Tube

  • Comparing the density of two liquids
  • Determining the density of a liquid by knowing the density of another liquid
  • Determining the relative density of a liquid that does not mix with water (immiscible liquid)

U-Tube Types

  • More than two liquids: P_A = P_B, ρ₁h₁ = ρ₂h₂ + ρ₃h₃
  • Two liquids: P_A = P_B, ρ₁h₁ = ρ₂h₂

Barometer

  • A glass tube of length 1 m opened at one end
  • A tank of suitable volume
  • A suitable volume of mercury

Idea

  • Pressure is the same at all points in the same horizontal plane in a static homogeneous liquid.
  • Pressure at point (A) = Pressure at point (B).

Uses

  • Measuring atmospheric pressure
  • Determining the height of a mountain or a building

Formulas

  • Pa = PA = ρgh
  • ΔP(mercury) = ΔP(air) is PHg g (h₁ - h₂) = Pair ghmountain

Capillary Tube

Formulas

  • ρ = Pa - h
  • ρ = Pa + h
  • ρ = Pa

Manometer

  • Structure: Includes a gas
  • Idea: Pressure at all points in the same horizontal plane in a static homogeneous liquid is the same.
  • Types: Water manometer and mercury manometer

Uses

  • Measuring the pressure of enclosed gas
  • Measuring the difference between the pressure of enclosed gas and the atmospheric pressure

Formulas

  • If the liquid level in the free end branch is the same as the level in the other branch, then: ΔP = 0
  • If the liquid level in the free end branch is higher than the liquid level in the other branch, then: ΔP = + ρgh (N/m²) or ΔP = +h (cmHg) if using mercury
  • If the liquid level in the free end branch is lower than the liquid level in the other branch, then: ΔP = -ρgh or ΔP = -h (cmHg) if using mercury

Pascal's Principle

Formulas

  • Two points are at different levels: P₁ = P₂, f/a + ρgh = F/A
  • Two pistons are at the same level: P₁ = P₂, f/a = F/A

Mechanical Advantage of Hydraulic Press

  • η = A/a = R²/r² = y₁/y₂
  • Efficiency = (Work done at big piston) / (Work done at small piston) = (Fy₂)/(Fy₁)

Laws of Gases

Boyle's Law

  • At constant temperature, the volume of a fixed mass of gas is inversely proportional to the pressure of the gas
  • P(Vol) = const (constant)
  • P₁/P₂ = (Vol)₂/(Vol)₁

Charles's Law

  • At constant pressure, the volume of a fixed mass of gas is directly proportional to its temperature on Kelvin scale
  • (Vol)/T = Const (constant)
  • (Vol)₂/(Vol)₁ = T₂/T₁

Pressure Law

  • At constant volume, the pressure of a fixed mass of gas is directly proportional to its temperature on Kelvin scale
  • PVol = Const (constant)
  • P₁/P₂ = T₁/T₂

General Gas Law

  • P₁ / (ρ₁T₁) = P₂ / (ρ₂T₂)

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