**Electric and Magnetic Fields and ****Capacitance**

designed by Dr T. Marlow

## Specification83 explain what is meant by an electric field and recognise and use the expression electric field strength
E = F/Q84 draw and interpret diagrams using lines of force to describe radial and uniform electric fields qualitatively. Demonstration of electric lines of force between electrodes 85 use the expression F = kQ1Q2/r^2, where k = 1/4πε0 and derive and use the expression E = kQ/r^2 for the electric field due to a point charge. Use electronic balance to measure the force between two charges86 investigate and recall that applying a potential difference to two parallel plates produces a uniform electric field in the central region between them, and recognise and use the expression E = V/d87 investigate and use the expression C = Q/V. Use a Coulometer to measure charge stored88 recognise and use the expression W = ½ QV for the energy stored by a capacitor, derive the expression from the area under a graph of potential difference against charge stored, and derive and use related expressions, for example, W = ½ CV^2. Investigate energy stored by discharging through series/parallel combination of light bulbs89 investigate and recall that the growth and decay curves for resistor–capacitor circuits are exponential, and know the significance of the time constant RC90 recognise and use the expression Q = Q0 e^(-t/RC) and derive and use related expressions, for exponential discharge in RC circuits, for example, I = Io e^(-t/RC)Use of data logger to obtain I-t graph 91 explore and use the terms magnetic flux density B, flux Φ and flux linkage NΦ92 investigate, recognise and use the expression F = BIl sin θ and apply Fleming’s left hand rule to currents93 recognise and use the expression F = Bqv sin θ and apply Fleming’s left hand rule to charges. Deflect electron beams with a magnetic field94 investigate and explain qualitatively the factors affecting the emf induced in a coil when there is relative motion between the coil and a permanent magnet and when there is a change of current in a primary coil linked with it. Use a data logger to plot V against t as a magnet falls through a coil of wire 95 investigate, recognise and use the expression ε = - d( NΦ)/dt and explain how it is a consequence of Faraday’s and Lenz’s law |