Physics: Energy Stores & Specific Heat Capacity PDF

# Physics ## Energy stores | Energy store | Objects with energy in this store | |---|---| | Kinetic | Anything moving has energy in its kinetic energy store. | | Thermal | Any object. The hotter it is, the more energy it has in this store. You may also see thermal energy stores called internal ene...

# Physics ## Energy stores | Energy store | Objects with energy in this store | |---|---| | Kinetic | Anything moving has energy in its kinetic energy store. | | Thermal | Any object. The hotter it is, the more energy it has in this store. You may also see thermal energy stores called internal energy stores. | | Chemical | Anything that can release energy by a chemical reaction, e.g. food, fuels. | | Gravitational Potential | Anything that has mass and is inside a gravitational field. | | Elastic Potential | Anything that is stretched (or compressed) e.g. springs. | | Electrostatic | Anything with electric charge that is interacting with another electric charge - e.g. two charges that attract or repel each other. | | Magnetic | Anything magnetic that is interacting with another magnet - e.g. two magnets that attract or repel each other. | | Nuclear | Atomic nuclei have energy in this store that can be released in nuclear reactions. | ## Specific heat capacity Specific heat capacity is the amount of energy needed to raise the temperature of 1 kg of a substance by 1 °C. $ΔE = mcΔΘ$ - $ΔE =$ change in thermal energy (J) - $m =$ mass (kg) - $ΔΘ =$ temperature change (°C) - $c =$ specific heat capacity (J/kg°C) ## Core practical: Investigating specific heat capacity **Diagram:** A diagram shows a simple experiment setup for investigating specific heat capacity. It includes the following components: - A power supply connected to a heater. - A heater placed beneath a block of insulation material. - A thermometer placed on top of the block. - An ammeter connected to the circuit. **Instructions:** 1. Use the current and voltage reading to calculate power. 2. Use the calculated power to calculate how much energy has been transferred by the heater. 3. Assuming no energy has been dissipated, you can plot a graph of temperature change (ΔΘ) against energy transferred (ΔE). **How to find specific heat capacity:** You can find the specific heat capacity of the block using the gradient of the linear part of the graph. The gradient is $ΔΘ/ΔE$, so since $ΔE = mcΔΘ$, the gradient is $1/mc$. So the specific heat capacity of the material of the block is: $1/(gradient * mass of the block)$. ## Energy transfer for falling objects When something falls, energy from its gravitational potential energy store is transferred to its kinetic energy store. The further it falls, the faster it goes. For a falling object when there's no air resistance, you can use the principle of conservation of energy to get: - Energy lost from the g.p.e. store = Energy gained in the kinetic energy store **Diagram:** A diagram shows a flowchart illustrating the energy transfer process for falling objects: - **Start:** Gravitational potential energy (Eg) - **Conversion:** Downward arrow labeled "$g =$ gravitational field strength (N/kg), $h =$ height (m), $m =$ mass (kg)" leading to $E_g = mgh$ - **Conversion:** Downward arrow labeled "$v =$ speed (m/s), $m =$ mass (kg)" leading to $E_k = 1/2 mv^2$ - **End:** Kinetic energy ($E_k$). **Description:** Work done is energy transferred from one store to another. The principle of conservation of energy states that energy can be transferred usefully, stored, dissipated but never created or destroyed. Power is the rate of energy transferred. $Efficiency = (useful power output) / (total power input)$