Physics: Mass, Volume, and Thermal Conductivity

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Questions and Answers

What is the main effect of heating on the resistance of a wire?

It decreases the resistance.

It increases the resistance. (correct)

It remains constant regardless of temperature.

It only affects the resistance in alternating current.

Which term describes a systematic error indicated by a measuring instrument reading a value when it should be zero?

Random error

Calibration error

Zero error (correct)

Human error

What is the frequency of alternating current (AC) in the UK?

25Hz

50Hz (correct)

60Hz

100Hz

What does the term 'potential difference' refer to in the context of electrical circuits?

The amount of energy used per unit charge Signup and view all the answers

What is the effect of using a low potential difference (P.D) while taking measurements?

It reduces the effects of heating. Signup and view all the answers

How is resistance related to the length of the wire?

It is directly proportional. Signup and view all the answers

Which defines the time taken for the current to change direction and back once in an AC supply?

Cycle time Signup and view all the answers

What is the primary use of a transformer with alternating current (AC)?

To increase or decrease the potential difference. Signup and view all the answers

What is the importance of using the same mass of insulating material each time in the experiment?

To maintain consistency in thermal conductivity tests Signup and view all the answers

What should be done if the thermometer bulb is not submerged in water during the experiment?

The temperature readings will be inaccurate Signup and view all the answers

Why is it necessary to plot a cooling curve from the recorded temperature results?

To visualize the rate of temperature change over time Signup and view all the answers

What is the purpose of using cardboard with a small hole as a lid for the large beaker?

To trap steam and prevent evaporation Signup and view all the answers

What is the initial step before recording the temperature of the water in the experiment?

Transferring the designated volume of hot water into the smaller beaker Signup and view all the answers

What is the first step in determining the mass of an object using a balance?

Set the balance to 0.0 Signup and view all the answers

How is the volume of a regular object calculated?

By multiplying the length, width, and height Signup and view all the answers

When measuring the volume of an irregular object using a eureka can, what should be done to avoid spilling water?

Carefully place the object into the can Signup and view all the answers

What role does cavity wall insulation play in buildings?

Decreases thermal energy transfer Signup and view all the answers

Which of the following materials is used to reduce thermal energy loss through windows?

Double glazed windows Signup and view all the answers

What is a common source of inaccuracies when measuring the volume of water displaced?

Spilling water during the process Signup and view all the answers

How can thermal energy loss through the roof be effectively reduced?

By using loft insulation Signup and view all the answers

What happens if the balance is not set to 0.0 before weighing?

The measurement will be inaccurate Signup and view all the answers

Which of the following describes a potential risk when conducting the mass measurement experiment?

Falling hazard due to improper placement Signup and view all the answers

To achieve a more accurate volume measurement, what should be done after measuring the displaced water?

Repeat the measurement multiple times Signup and view all the answers

What method can be used to reduce human error when transferring water from a kettle to a beaker?

Pour the water slowly Signup and view all the answers

Which of the following reduces heat conducted when cooking?

Using plastic walls and lids Signup and view all the answers

What is the formula for calculating power in terms of energy transferred?

Power = Energy transferred / Time Signup and view all the answers

Which appliance primarily converts electrical energy into kinetic energy?

Blender Signup and view all the answers

What component is used to prevent excessive current in a circuit?

Fuse Signup and view all the answers

What happens to the resistance of a thermistor as temperature increases?

Resistance decreases Signup and view all the answers

Which of the following statements about conventional current is true?

It flows from positive to negative Signup and view all the answers

In a series circuit, how does the current behave?

It remains constant throughout Signup and view all the answers

What effect does insulation have in energy efficiency?

Reduces waste energy Signup and view all the answers

What does potential difference in an electrical circuit do?

Drives the flow of current Signup and view all the answers

Which device gives off light when current flows through it?

Light Emitting Diode (LED) Signup and view all the answers

What type of energy transformation occurs in a kettle?

Electrical to thermal energy Signup and view all the answers

Why is efficiency important in energy use?

To maximize useful energy output Signup and view all the answers

When is the resistance of a variable resistor changed?

By adjusting a slider Signup and view all the answers

What is the primary function of an iron core in a transformer?

To increase the strength of the magnetic field Signup and view all the answers

Which type of transformer increases the potential difference (P.D)?

Step-up transformer Signup and view all the answers

Why is AC preferred for transformers over DC?

AC allows for easy voltage conversion Signup and view all the answers

What equation represents the conservation of power in a transformer?

P1 = P2 Signup and view all the answers

What happens if the earth wire in a mains electricity setup is not connected properly?

A person can be electrocuted Signup and view all the answers

What is the role of the fuse in a mains supply?

To melt in case of high current flow Signup and view all the answers

Why does a transformer require a changing magnetic field?

To induce a potential difference Signup and view all the answers

What is one of the main functions of the neutral wire in a mains setup?

To return current back to the source Signup and view all the answers

How does the National Grid minimize energy losses during transmission?

By implementing step-up transformers Signup and view all the answers

What potential difference is commonly used in household appliances?

230V Signup and view all the answers

What is a significant risk when touching a live wire?

It can result in an electric shock Signup and view all the answers

What type of transformer has fewer turns in the secondary coil compared to the primary coil?

Step-down transformer Signup and view all the answers

Which wire in the three-cord cable has a potential difference of 0V?

Neutral wire Signup and view all the answers

What is the recommended action for electricians when working with the mains supply?

Switch off the mains supply Signup and view all the answers

Study Notes

Determining Object Mass and Volume

Regular objects: Mass is determined using a balance; volume is calculated by multiplying length, width, and height. Density is mass divided by volume.
Irregular objects: Mass is determined using a balance. Volume is measured by water displacement in a eureka can and measuring cylinder. Density is mass divided by the displaced water volume. Repeat measurements and calculate the mean for improved accuracy.
Sources of inaccuracy: Water spillage, balance inaccuracy, incomplete water displacement, and falling hazards. Care should be taken to minimize these.

Thermal Conductivity in Buildings

Modern houses have two-layered walls (brick and breezeblock with a cavity). High thermal conductivity of these walls leads to energy loss and increased heating costs.
Cavity wall insulation (low thermal conductivity material) reduces energy loss.
Double-glazed windows and loft insulation also reduce energy loss by minimizing convection and heat transfer.
Thicker walls reduce the rate of thermal energy transfer.

Thermal Insulator Practical

Experiment setup: Two beakers (small inside large), hot water, cardboard lid with thermometer hole, stopwatch, insulating materials.
Procedure: Measure water temperature at 3-minute intervals for 15 minutes. Repeat with various insulating materials (same mass). Plot a cooling curve.
Newspaper experiment: Repeat the above, adding layers of newspaper to observe the effect on cooling rate.
Sources of Inaccuracy: Inconsistent initial water temperature, human error during water transfer, timing errors, and inconsistent insulator mass. Minimizing these errors will increase experimental accuracy.

Efficiency

Efficiency is calculated as (useful energy output / total energy input) or (useful power output / total power input).
Efficiency improvements include using wider-based pans with lids, strategically placed heating elements, plastic walls/lids, lubrication (mechanical devices), and insulation.

Electricity and Electrical Appliances

Power (Watts or J/s) is the rate of energy transfer or work done. Power = Energy transferred/Time = Work done/Time = Voltage x Current = Current² x Resistance.
Appliances and their energy conversions:
- Blender, fan, hairdryer: Electrical energy to kinetic energy (with thermal energy waste).
- Kettle, iron: Electrical energy to thermal energy.
- Lamp: Electrical energy to light energy (with thermal energy waste).
- Refrigerator, washing machine, toaster: Various energy conversions depending on the appliance function.

Circuits and Components

Circuit components: Cell, battery, voltmeter, ammeter, filament bulb/lamp, open/closed switch, fuse, light-dependent resistor (LDR), variable resistor, thermistor, diode, light-emitting diode (LED), resistor.
Potential difference (voltage): The force driving current flow. 0 volts means no force and no work done.
Current: The rate of charge flow (flow of electrons). Conventional current is depicted as flowing from positive to negative, despite electrons' actual flow in the opposite direction.
More energy leads to higher voltage (greater potential for energy transfer).
Series circuits: Current remains constant throughout the circuit.

Charge, Current and Time

Relationship between charge (coulombs), current (amperes), and Time (seconds): Current = Charge/Time

Direct and Alternating Current (AC/DC)

Direct current (DC) flows in one direction only.
Alternating current (AC) constantly changes direction; in the UK, it does this 50 times per second (50 Hz).
UK mains AC has a potential difference (PD) of approximately 230V.
AC is easier to transform to increase or decrease PD.

Transformers

Transformers only work with AC due to the need for a changing magnetic field to induce a PD.
They consist of a primary and secondary coil around an iron core.The coils are electrically separate.
A changing magnetic field in the primary coil induces a PD in the secondary coil.
Step-up transformers increase PD (more turns in secondary coil).
Step-down transformers decrease PD (fewer turns in secondary coil).
PD relationship: V_p/V_s = N_p/N_s (where V is PD and N is number of turns).
Power is conserved in an ideal transformer: P_p = P_s (power in primary = power in secondary).

Mains Electricity and Safety

Mains electricity is AC.
Three-core cables: live wire (230V), neutral wire (0V), and earth wire (0V).
The earth wire provides a low-resistance path to ground, preventing electric shock.
The fuse in the plug melts if a large current flows due to a fault, breaking the circuit.
Even when switched off, the live wire remains at 230V and presents a shock hazard.
Copper wires are used for their conductivity.
PVC insulation prevents shock.

The National Grid

The National Grid uses step-up transformers to increase PD to 400kV for efficient long-distance transmission (reducing current and heat loss).
Step-down transformers reduce PD to 230V for safe household use.
Electricity is generated at 25kV.

Experimental Sources of Inaccuracy

Zero error in measuring instruments is a systematic error, requiring subtraction from all readings.
Heating effects in wires increase resistance, minimized by using a low PD or applying current only during measurements.

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Description

Explore the principles of determining mass and volume of both regular and irregular objects, emphasizing the importance of accuracy and sources of inaccuracy. Additionally, learn about the impact of thermal conductivity in building design and the ways to minimize energy loss through insulation techniques.