The German physicist Heinrich Hertz (1857–1894) was the first to generate and detect certain types of electromagnetic waves in the laboratory. Starting in 1887, he performed a series of experiments that confirmed the existence of electromagnetic waves and verified that they travel at the speed of light. Hertz used an alternating-current RLC (resistor-inductor-capacitor) circuit that resonated at a known frequency and connected it to a loop of wire. High voltages induced across the gap in the...

Sigmund Freud, an Austrian neurologist born in 1856, significantly influenced psychology through his exploration of the unconscious mind. His interest in patients suffering from hysteria and neurosis — conditions without apparent physical causes — led him to theorize the existence of an unconscious mind, a repository for feelings and urges beyond our awareness. Freud's innovative approach included techniques such as dream analysis, free association, and attention to slips of the tongue to...

Elisabeth Kübler-Ross significantly advanced psychology's understanding of the process of dying with her influential book, On Death and Dying (1969). She focused on studying terminally ill individuals and outlined five stages commonly experienced when coping with death: denial, anger, bargaining, depression, and acceptance.
In denial, individuals reject the reality of their condition, often thinking, "This isn't true; I feel fine," as a way to protect themselves from emotional distress. Anger...

There are two ways to determine the amount of heat involved in a chemical change: measure it experimentally, or calculate it from other experimentally determined enthalpy changes. Some reactions are difficult, if not impossible, to investigate and make accurate measurements for experimentally. And even when a reaction is not hard to perform or measure, it is convenient to be able to determine the heat involved in a reaction without having to perform an experiment.

Gestalt psychology, founded by Max Wertheimer, Kurt Koffka, and Wolfgang Kohler, emphasizes the importance of understanding perception as an organized whole. Developed as a counter to Wilhelm Wundt's structuralism, this approach posits that our perceptions are more than just the sum of sensory parts; they are comprehensive wholes where the relationships between parts define the perception. The principle "The whole is greater than the sum of its parts" encapsulates this view, illustrating how...

Karen Horney's psychoanalytic theories emphasize the potential for self-realization and the importance of addressing social and cultural, rather than biological, factors in personality development. She challenged traditional Freudian views, particularly Freud's concept of "penis envy," which she argued stemmed from cultural influences rather than inherent biological differences. Horney believed that any sense of inferiority in women was a result of societal conditioning, such as dependence on...